you're looking for legal advice from a forum about men's clothes...find a lawyer There seems to be quite a number of lawyers on this forum actually hahaha. If you're interested in being a "gentleman" you should offer to take the car back and return her money. If you're interested in being a used car salesman then all the above advice applies. Honestly, a clunk in the transmission is not right. You should get that fixed before you sell privately. If you don't want to do that then sell it to a dealer--they will know what an "intermittent clunk" could mean and pay you accordingly. You may not have any legal responsibility but that does not mean you are morally correct. I don't see anything morally wrong about it. He did all that he could reasonably do already: sought professional opinion from his mechanic and raised the issue with her. And according to his mechanic the car is fine. Bordeline is not an expert automechanic and he did not sell her a lemon base on the information he has on the car. It is also her responsibility to make sure to double check the car is fine before purchasing and she would be morally wrong if she expect him to cover the repair costs due to her own negligence. There are two parties in the trade and both have their own responsibilities. It would also be quite irrational if he had gone and paid $2000 for repairing something that may not really be all that serious anyway to then sell it for only $1000 extra.