That's horrible. Sorry to hear. I guess he got your key coppied in the small amount of time he had it. In reality it sounds like a pretty good setup if you were really thinking. Give someone a dud so they'll at the very least want the item they traded back so they could get rid of the peice of shit someone just gave them....If that was truely there intention then it's quite brilliant. And maybe he was expecting you to bitch to him and when you decided to eat his lack of disclosure he decided to contact you instead to complain about something.
Could be the case but at the same time you never know. It is a crazy world we live in.