Plaintiff, General Motors Corporation (gm), appeals from the Court of Appeals decision that defendant, Department of Treasury, could impose use tax1 on the vehicle components and parts plaintiff provided to customers as part of plaintiff’s goodwill adjustments policy. We reverse the decision of the Court of Appeals and hold that assessment of use tax on the goodwill adjustments was improper because they were taxed pursuant to the General Sales Tax Act2 when customers purchased vehicles at retail.

I

When customers purchase new GM automobiles, they are provided with a GM limited manufacturer’s warranty. These limited manufacturer’s warranties provide, in pertinent part, for the replacement of defective parts of the automobile under certain circumstances. They also generally provide coverage for an expressly stated length of time, subject to earlier expiration, if the vehicle is driven for a certain number of miles. The department acknowledges that parts provided under these limited warranties are not sub*234ject to use tax because the customers paid for the right to replacement parts under the warranties at the time of the retail sale.

In addition to the limited warranties, GM provides a more open-ended “goodwill” adjustment policy under which GM will, on a discretionary basis, pay for replacement parts for GM vehicles even after the limited warranty period has expired. Although not referred to by name as a “goodwill adjustment policy,” notice of this policy is contained in the General Motors warranty manual provided to customers at the time of sale. In this regard, the manual provides:

Should you ever encounter a problem during or after the warranty periods that is not resolved, talk to a member of dealer management. If the problem persists, follow the additional procedure outlined in “Owner Assistance,” on page 16 of this booklet. [Emphasis added.]

The Owner Assistance section of the manual outlines a “Customer Satisfaction Procedure.” It states that problems will “normally” be resolved by the dealer’s sales or service departments.3 However, if a concern is not resolved at that level, the manual rec*235ommends first discussing the problem with the dealership management. If the problem is not resolved by the dealer management, customers are told to contact GM directly. A customer dissatisfied with the outcome of the procedure may elect arbitration. The manual states that, while a customer is not bound to accept the result of the arbitration proceeding, GM will “generally” agree to be bound by it even though it reserves the right to terminate its participation in the arbitration program.4

The department conducted an audit of gm’s compliance with Michigan tax laws for the period of January 1, 1986, through December 31, 1992. As a result of the audit, the department assessed against GM use taxes and interest of $5.5 million on the vehicle components and parts provided by GM to customers as goodwill adjustments. The department had not previously assessed such a tax. During the audit period, GM customers in Michigan obtained $82 million in components and parts under the goodwill policy.

Gm appealed the assessment to the Court of Claims. In pertinent part, GM alleged that the department lacked the statutory authority to impose use tax on goodwill adjustments because sales tax was imposed on the cost of the goodwill adjustments when vehicles were sold at retail. However, the Court of Claims disagreed with gm’s position and granted summary disposition in favor of the department pursuant to MCR 2.116(C)(10), holding, in relevant part, that the transfer of parts under the goodwill program is sub*236ject to use tax. The Court of Appeals affirmed regarding this issue,5 concluding that “plaintiff’s dealers were not obligated to provide all customers with goodwill adjustments” and, therefore, that the “value of the goodwill program was not included in the gross proceeds arising from the retail sales of plaintiff’s vehicles.”6 The Court of Appeals also emphasized its view that the purchasers of gm vehicles did not obtain “any enforceable rights in the goodwill program.” We granted leave to appeal.

II

Because the essential facts are not in dispute, we are presented with a question of law: whether replacement parts provided to customers at gm’s expense through the goodwill program are independently subject to Michigan’s use tax in connection with the transfer of the parts. We review questions of law de novo. Kelly v Builders Square, Inc, 465 Mich 29, 34; 632 NW2d 912 (2001). This is the same standard of review applicable to the grant of a motion for summary disposition. MacDonald v PKT, Inc, 464 Mich 322, 332; 628 NW2d 33 (2001).

*237III

The sales tax and the use tax are interrelated. Sales tax is imposed by the General Sales Tax Act (gta) on the gross proceeds of a business. MCL 205.52(1). The gta defines “[g]ross proceeds” as the “amount received in money, credits, subsidies, property, or other money’s worth in consideration of a sale at retail____” MCL 205.51(l)(i). In contrast, pursuant to the Michigan Use Tax Act (uta), use tax is generally imposed on the privilege of “using, storing, or consuming tangible personal property.” MCL 205.93(1).

Gm contends that the cost of its goodwill adjustments is exempt from use tax under § 4(1) (a) of the UTA. MCL 205.94(l)(a) provides that “[property sold in this state on which transaction a tax is paid under the general sales tax act” is exempt from the use tax “if the tax was due and paid on the retail sale to a consumer.” Thus, our inquiry is whether “tax was due and paid” pursuant to the gta on the cost of the goodwill adjustments when vehicles were sold at retail.

The sales and use taxes, while imposed in different ways, do not operate in isolation. Rather, provisions of the uta and the gta are supplementary and complementary. World Book, Inc v Treasury Dep’t, 459 Mich 403, 408; 590 NW2d 293 (1999); Elias Bros Restaurants, Inc v Treasury Dep’t, 452 Mich 144, 153; 549 NW2d 837 (1996). Uta § 4(1)(a)’s exemption is an expression of a legislative intent to avoid pyramiding of sales and use tax. Elias Bros, supra. In other words, a transfer of property that has already been subjected to Michigan’s sales tax is not subject to this state’s use tax. As directed by § 4(l)(a), we examine the provisions of the GTA to determine whether tax *238was paid on the goodwill adjustment at the retail sale to a customer or whether the department’s assessment of use tax was appropriate.

The gta defines a “sale at retail” as “a transaction by which the ownership of tangible personal property is transferred for consideration, if the transfer is made in the ordinary course of the transferor’s business and is made to the transferee for consumption or use, or for any purpose other than for resale . . . .” MCL 205.51(1)(b). The question is thus whether the goodwill adjustment policy is consideration flowing to customers when they purchase a gm vehicle or merely an illusory promise. Stated otherwise, we examine whether the cost of the goodwill adjustment policy is included in the retail price of GM vehicles as something that is purchased by customers.

At the time of retail sale, gm customers receive an owner’s manual. The manual invites customers to initiate a dialogue with the dealership when a defect arises, “during or after the warranty periods.” The manual states the goal of resolving the defect to the “customer’s satisfaction.” Gm admits that its customers are not guaranteed that requested after-warranty goodwill adjustments will be made. Indeed, gm suggests its dealers negotiate with customers for copayment on goodwill adjustments case by case.7 Nevertheless, gm’s goodwill policy is a promise to hear and address customer complaints even after the written warranty expires.

To have consideration there must be a bargained-for exchange. Higgins v Monroe Evening News, 404 Mich 1, 20-21; 272 NW2d 537 (1978). There must be *239“ ‘a benefit on one side, or a detriment suffered, or service done on the other.’ ” Plastray Corp v Cole, 324 Mich 433, 440; 37 NW2d 162 (1949). Courts do not generally inquire into the sufficiency of consideration, Harris v Bond & Mtg Corp, 329 Mich 136, 145; 45 NW2d 5 (1950). It has been said “[a] cent or a pepper com, in legal estimation, would constitute a valuable consideration.” Whitney v Steams, 16 Me 394 (1839). The owner’s manual provided at the time of sale invites customers to voice complaints even after the warranty period ends, with the goal of resolving the complaint to the customer’s satisfaction. We hold that this opportunity for dialogue and possible resolution of complaints—even outside the warranty period—is a benefit flowing to purchasers of GM vehicles at the time of retail sale and, therefore, is consideration for the sale.8 Therefore, replacement parts provided pursuant to the goodwill program are subject to the sales tax at the time of retail sale and are exempt from the use tax under § 4(l)(a) of the uta.9

*240Gm’s promise pursuant to its goodwill adjustments policy, while discretionary with respect to whether there will be any “adjustment,” is not discretionary regarding gm’s obligation to act reasonably and in good faith in response to a customer complaint.10 Reinforcing this contractual undertaking to act in good faith is MCL 440.1203, part of Michigan’s version of the Uniform Commercial Code. MCL 440.1203 provides that “[e]very contract or duty within this act imposes an obligation of good faith in its performance or enforcement.”11 This means that, should GM not consider complaints under the goodwill adjustment policy in good faith, it can be sued.

The dissent agrees that a unilateral or discretionary promise could “constitute valid consideration.” Post at 245. However, the dissent would decline to rule that gm’s promise is valid consideration in part because gm’s customers have “little if any” knowledge of the scope of gm’s discretion. Id. That it is unknown how liberally GM will exercise its discretion does not mean there is no discretion. In fact, it means there is discretion, i.e., a benefit to the consumer.12 The dis-

*241sent has fallen into the error of considering not merely if there is consideration, but its sufficiency. As we have stated, courts do not inquire into the adequacy of consideration to support a contract. Higgins, supra.13 Thus, we conclude that the duty the goodwill policy imposes on GM to consider requests for redress in good faith is a valuable consideration that is worth far more than the legendary peppercorn.14

Moreover, the evidence indicates that for the period 1986-1992, plaintiff provided “goodwill” parts to customers of General Motors cars having an estimated value of $82 million. As the dissent itself recognizes, “the cost of . . . [these] parts has been factored into the retail cost of the car . . . .” Post at 247. If this is so, then such costs have been necessarily paid by the consumer at sale, i.e., a car otherwise valued at $9975 has been increased in price to $10,000 and the *242consumer has paid an additional $25 for the goodwill policy. Plaintiff, not being a charitable institution, must necessarily have factored the cost of the goodwill policy into the cost of the car, and such cost must necessarily have been paid by the consumer. Further, it can be presumed that the consumer paid $25 because something of value passed. The automobile industry is sufficiently competitive that few companies can afford to tack costs onto their products for parts or services that are perceived as valueless by their consumers. Contrary to the dissent, we can easily envision a “rational, self-interested market participant” paying something for a benefit estimated to provide more than $13 million in annual benefits to consumers. Our interpretation of MCL 205.94(l)(a) does not constitute a “lax” interpretation of consideration as the dissent asserts. Post at 248. Rather, our interpretation is based on fundamental contract principles and reflects the realities of the marketplace.15

IV

Because the goodwill adjustment policy provides an opportunity for GM customers to seek redress of vehicle defects and because the policy is included in the retail price of GM vehicles and purchased at the time of retail sale, it is part of the consideration flow*243ing to gm customers when they purchase a gm vehicle that is taxed pursuant to the gta at retail sale. We reverse the decision of the Court of Appeals and remand this case to the Court of Claims for entry of judgment in favor of gm.

(dissenting). I write separately to express my disagreement with the majority’s conclusion that retail new car customers exchange consideration for goodwill policy parts when purchasing vehicles manufactured by plaintiff. Plaintiff has claimed its goodwill repair parts should not be subject to use tax because the costs are included in the price of the vehicle, which is subject to sales tax. Under MCL 205.94(l)(a), no use tax is owed on retail sales subject to sales tax. However, this exemption applies only if the parts are included in a “sale at retail,” i.e., “a transaction by which the ownership of tangible personal property is transferred for consideration. . . .” MCL 205.51(l)(b). Because I cannot agree that the goodwill parts are transferred for consideration, I must respectfully dissent.

I

Plaintiff directs its dealers to make goodwill adjustments case by case “where special consideration is in order to enhance customer satisfaction and loyalty.”1 Most dealers have the discretion to provide repair parts free or at a reduced rate to consumers after the *244original warranty expires.2 These repairs are provided to select customers who are unsatisfied with defective parts after the manufacturer’s warranty expires.

Consumers are not given any general or specific information concerning the goodwill program and are informed in the warranty manual of their right to contact plaintiff after the manufacturer’s warranty expires if they are dissatisfied with the dealer’s offered resolution. The written warranty also indicates that arbitration proceedings may be an option.3 In essence, the consumer is given an opportunity to ask for free repair parts, but has no legal right to any specific repair and knows nothing of the goodwill policy program in general, or of its specific terms. Though plaintiff may agree to subject itself to arbitration pro*245ceedings, consumers gain no legally enforceable right as a result of this program, a program purportedly “purchased” at the retail sale.

Consideration requires bargained-for legal detriment. Higgins v Monroe Evening News, 404 Mich 1, 20-21; 272 NW2d 537 (1978) (opinion by Blair Moody, Jr., J.). I agree with the majority that a discretionary promise must be exercised in good faith and that the reasonable execution of such a promise may constitute valid consideration. J R Watkins Co v Rich, 254 Mich 82, 84-85; 235 NW 845 (1931); Wood v Lucy, Lady Duff-Gordon, 222 NY 88; 118 NE 214 (1917). However, I am not convinced that plaintiff’s good-faith exercise of its discretionary power is sufficient to permit a finding of bargained-for consideration in this instance. A party relying on the good-faith exercise of another’s unilateral discretion generally has some knowledge of the scope of discretion involved and the potential benefits that might accrue. In this case, customers have little if any knowledge of what they allegedly bargained and paid for at the retail sale. I cannot fathom what rational, self-interested market participant would actually bargain for and purchase such a promise. If it came free with the purchase price, most would accept it, but almost no one would buy it.

Further, I am not sure that an arbitrator would have any reason to rule in favor of a customer if dissatisfaction actually resulted in an arbitration hearing. On the basis of the contract between the parties, the express warranty would have expired if a customer requested parts under the goodwill policy. The simple failure to purchase a supplemental warranty suggests plaintiff has absolutely no legal or good-faith duty to *246repair defective parts after the warranty expires. The presence of express promises (original warranty) and the opportunity to purchase supplemental promises (extended warranty) evidence the parties’ intention that plaintiff escape liability for defects after the original warranty period expires. Because information concerning the terms of the goodwill policy is generally kept secret, I am not sure that a consumer could adequately plead his case to the arbitrator, assuming plaintiff agreed to participate. All a consumer is left with is the right to complain to plaintiff, and I believe it is a stretch to consider that sufficient consideration where such a right exists regardless of the goodwill policy. Therefore, I would hold that the goodwill policy adjustment program does not constitute valid consideration.4

*247Even so, I agree that the cost of the goodwill policy parts has been factored into the retail cost of the car, and to that extent the goodwill parts are subject both to use and sales tax. Unfortunately, because the use tax statute exempts only costs transferred for consideration in a retail sale, the Legislature essentially failed to avoid pyramiding taxes where costs are factored into a product, but are not actually part of the consideration paid. MCL 205.51, 205.94(1)(e).5

II

I suspect the most appropriate and forthright method to analyze the goodwill program for tax purposes would be to conceive of the parts as promotional or gratuitous items. Plaintiff grants adjustments *248“in order to enhance customer satisfaction and loyalty.” In essence, the goodwill policy is a select form of advertising, i.e., a large scale version of the distribution of free pens and cups to conference participants or the provision of free pharmaceutical samples to physicians. Dealers probably grant the benefits of the discretionary goodwill program to those customers most likely to experience enhanced manufacturer loyalty. Because the program most resembles a marketing or customer satisfaction offer, and because there is no general statutory exemption for promotional items from use tax in Michigan,6 I would permit defendant to assess use taxes, assuming it does so in a uniform fashion. See Virginia Dep’t of Taxation v Miller-Morton Co, 220 Va 852, 859; 263 SE2d 413 (1980) (when a distributor of products withdrew products from inventory within the state for free disposition to customers also within the state, the distributor exercised a power incident to ownership of the products, and this use of products previously held for resale was not within the exemption from use tax).

III

The majority permits a lax interpretation of consideration in order to bridge the gap between the text of the statute and the general desire to avoid duplicate *249taxation. While the end might be worthwhile, the method arguably creates an empty definition of consideration that could affect future bargainers. Rather than compensate for the legislative failure to exempt all product costs from use tax by watering down our understanding of consideration, I would hold that the repair parts are not included in the retail sale for which consideration is paid.