Case:

Ruling: The rule that the Shulchan Aruch (Choshen Mishpat 232:6) sets down is that the grounds for mekach ta’ut (voiding a sale because of a blemish) depend on the practice of the people of the place. Nevertheless, the Terumat Hadeshen (322) says that one who wanted to buy meat from a castrated animal (which is supposed to taste and smell better) and received a non-castrated one cannot void the sale because the meat he got is edible, unless he is known to be very particular. The Bach and Shach (233:1) ask why this is different from one who wanted to buy good wheat and received bad wheat, as he is allowed to back out of the deal. The distinction is between one who received something which is objectively sub-par (where there is mekach ta’ut) and one who wanted something above average and received something average.
We find elsewhere, regarding the sale of a slave with certain blemishes, that if he is fit to do the job for which he was bought, the blemishes do not cause the sale to be voided. One can say that here too the car bought is fully fit to be driven. However, the Shulchan Aruch’s rule of following the local practice applies here as well, and even though the car can be driven, most people would consider the fact that the car was used for driving lessons as grounds for mekach ta’ut.
There is another ground for mekach ta’ut and that is the discrepancy in price. This is not simple, though, because when a seller is not a merchant but a regular consumer and sells one of the utensils he uses, the sale is not void due to overpricing because he wouldn’t have sold the item for its regular price (Shulchan Aruch, CM 227:23). (It may be different if the buyer did not know the seller was not a merchant.) Rashi explains that it is as if the seller made a condition that there will not be laws of overpricing. Although a car could fit into this category, it is more logical to say that since many people sell their car at some point, it is not an unusual event that would have the special laws of a non-merchant.