RE: What is my responsibility?
I'd actually like to hear the fully story here. You've only sold two items in the MarketPlace, Flyathome. It doesn't take a rocket surgeon to figure out what item you are talking about.
So, was there more time on the engine than he stated? Maybe he was honestly mistaken and didn't purposefully misrepresent the engine? Or, maybe he did purposefully misrepresent it, in which case I'd rather not deal with him - ever.
I think your responsibility is to confront him and get the truth about the whole situation. He's already sold the engine, so the point is moot. But, I would like to hear his side of the story before making my judgement.