The complaint alleges the sale of a motor and that the account therefor became due and payable within a reasonable time either by the return of the defective motor or by a payment in cash. The trial court did not regard the transaction as a sale to the defendants of a new motor, but as an exchange of parts of a motor car between the purchaser of the car and plaintiff pursuant to the terms of its contract of guaranty carried out through the agency of the defendants that the defendants breached their contract by failing to return the old motor, and plaintiff’s damages resulting therefrom were the value of the old motor and not the purchase-price of a new one. Were this the only transaction of its kind between plaintiff and defendants and had no bill been sent when the new motor was shipped, there would be good ground for limiting the damages to the value of the old motor. But the evidence shows that the custom of dealing in such-matters was to charge up to the defendants the agent’s price of the new part pending the return of the old, for which, when returned and accepted, a corresponding credit was-*339given. This custom of dealing was thoroughly understood and consented to by the defendants. The effect of it was equivalent to the plaintiff saying to the defendants and the latter agreeing thereto: Yon return the old defective part to us or pay us the price charged you for the new. The price •charged was the amount of damages agreed upon in case no return of the old part was made. Such a construction works no hardship upon dealers who return defective parts, and at ■the same time it adequately protects the manufacturer. ITe would in most cases be unable'to prove the value of the de-feetive part because of its having been out of his possession since new. And if the only penalty attached to a failure to return an old part was a payment of what a jury might assess its value, there would often be strong inducements to make purchases of old parts upon such terms. Under the ■custom of dealing between the parties the amount charged for the new part must be regarded as stipulated damages in case ■of a failure to return. The trial court was correct in construing the transaction not as a purchase and sale of a new motor, but as an exchange of parts under their contract. 'The error occurred in applying the wrong measure of damages. Under the evidence plaintiff was entitled to recover $4:10, the agent’s price of the new motor.

Upon the oral argument in this court counsel for plaintiff stated that if it was held plaintiff was entitled to recover $4:10 it would concede the amount of defendants’ first counterclaim in the sum of $182.15 and take judgment for the balance^ provided a good counterclaim was stated. Defend.ants in said counterclaim allege in substance that the Ott motor was defective through the fault of the plaintiff and that at its special instance and request they rendered services upon such machine of the reasonable value of $182.15. This states a good counterclaim. The allegation that the services were rendered at the special instance and request of the plaintiff leaves no room for its claim that under their contract the ■defendants were required to perform such services without *340cost to it. We must assume tliat defendants’ proof will be as broad as tbeir pleading in passing upon its sufficiency. The defendants, however, have interposed other counterclaims upon which they may desire to stand, so we cannot award judgment for the difference. But the defendants may have the option of submitting to a judgment against them for $227.85, the difference between $410 and $182.15, or a new trial.

By the Oourt.-, — Judgment reversed, and cause remanded for further proceedings in accordance with the opinion.