Q. A mail order clothing company promises: "If you are not completely satisfied with any item you buy from us, at any time during your use of it, return it and we will refund your full purchase price." Can I return items that are no longer wearable because of normal conditions such as stains and fraying?
A. Under Jewish law, every seller provides an unlimited money-back guarantee! Any object with a significant deficiency that was hidden from the purchaser can be returned whenever the deficiency is revealed – even after a period of years. The reason is that the entire sale is void, since the purchaser never intended to buy a defective item.
However, as soon as the defect is discovered, and the customer learns that the purchase was in error, he must stop using the object. Since he has decided the sale is void, the item doesn't belong to him! Using the item after the defect is discovered, or could easily have been discovered, implies that the purchaser doesn't mind this particular deficiency.
The mail-order seller you mention goes beyond the letter of the law. The company doesn't merely promise that the merchandise is free of defects; it guarantees that you will be completely satisfied with it. This means that if you discover something that you really don't like about the garment, even after a long time, you can still return it. For instance, if you bought a coat because you mistakenly thought it was waterproof but you don't get stuck in the rain with it until months later, you could still return it to this company.
However, a person doesn't regret buying a garment just because it eventually wears out! Therefore, you may not return something that is "not wearable because of normal conditions".
Even if there is a genuine source of dissatisfaction, you shouldn't use the garment after you decide to return it.
SOURCE: Shulchan Arukh Choshen Mishpat 332:3 and commentaries.