I am coming from the scam accusation topic from
DeonnnMutual characteristics between the 2 accounts.
I am not convinced that any of the characteristics you have listed are enough to make a definitive link between these two accounts. It seems to me that there is a not insignificant chance that you have just stolen $500 worth of bitcoin from an innocent third party.
I agree here that the evidences are not enough to keep his $500 and pretending that the other user was Deonnn.
@alterra57 I left you a tag from the other topic. I think you should send the BTC back to Deonnn if you are not interested to trade with him.