Look, you are all over-thinking this. Either this was a deposit to hold the rims...which you did, and therefore you have rendered the service for which he paid (so keep the money), or else he is arguing that it was NOT a deposit to hold the rims...in which case it was a nice gift from him.

He can't have it both ways. If he paid you a deposit to hold the rims, and you did so, then keep the damn money.

If he is now trying to back out on a technicality, then he is a douche bag, and your response should be, "Thank you for the early Christmas gift."

In any case, all of your emails should stress that you are still willing to live up to your part of the transaction. In other words, you're still willing to sell him the rims for the agreed-upon price minus the deposit. Otherwise, **** it. The cost of litigation will certainly exceed the cost of the rims, so you know he's bluffing.

Stick to your guns. I hate douche bags.