You don't have to accept the return, unless the terms of your sale specifically included a right of return/refund. Otherwise, he is obligated to pay you, and you may sue him for the money (such as in small claims court, acting as your own attorney to save on legal fees) as well as for any other costs you incured (such as the court filing fee; or if you incurred any fees when the check bounced). To win, you'd need to prove, such as with testimony (e.g. yours and your cousin's) that you delivered him a working tablet. If you did, the fact that he later decided he was unhappy with it is irrelevant. Of course, depending on how much money is at stake, it may be better to simply accept the tablet back and not sue, rather than spend hours on a lawsuit.