^^ Most likely. Either that he’s a complete ebay/online noob.
Personally I don’t think I’d buy an expensive motor over the Net… however, I have bought cars before so I guess I stand corrected. Even when I did though, I knew the risk at hand and that it is a completely different ball game than standard retail transactions.
Send the letter, tell him he was already partially refunded because of common business courtesy, but there’s no reason for you or the supplier to take a hit b/c he didn’t understand how the process works.