The money order is the proof. Even if it didn’t have the auction number on it, he has PROOF OF MONEY TRANSACTION. If he doesn’t have the goods, then he can request his money back unless some form of WRITTEN agreement was made concerning said money.
Nothing in writing? NO CASE FOR KEEPING THE MONEY. It would be harder to prove had he paid in cash, but if there is ANY papertrail, you are screwed if you can’t prove goods/service rendered.
The fact that it is a POSTAL MONEY ORDER makes it that much more pertinent that you RETURN THE MONEY. You do not want to fuck with the feds if the wheels get turning on this. You can try to be shady all you want, but don’t say you weren’t warned when you go to jail. Is $500 worth it?
Any lawyer will tell you the same thing. You are screwed if you don’t have it in writing with signature.
Real talk.
Jordan, do whatever you want, but I would STRONGLY advise you to give the money back unless you have documented and signed proof that the deposit was “non-refundable”.