That is a bit strange - why would the person be an original owner of something they also bought a used copy of? Sometimes I think people shop these sites enough to buy and sell pieces they feel they can make a profit on, and it would be quite possible to have bought more than one copy of something used that is turned around and sold. The situation you describe is hard to come up with an explanation for other than that the seller is mis-representing the piece
That said, I don't think there's much you can do or should try to do about it. As much as we all want this to be a completely honest environment, it probably isn't, and every buyer needs to do everything possible to protect themselves. If somebody claims to be the original owner and a buyer really cares about that, there are ways to verify the claim. -Kirk