Because you didnt send him the part. They arent going to give it back to him. Ive been there... on the wrong end. They took the money out of my account, never reimbursed the buyer. I then had to send the buyer a money order for the amount. He then closed the complaint, and paypal released the funds back to me. It takes 180 days before paypal will begin their investigation to release the money to the buyer... even though it takes them merly 10 days to take it from the seller. Thats because paypal keeps the money locked up in high interest yielding accounts to make more money. This is why I no longer use paypal... because they find ways to keep your money locked up if you do something wrong... and it screws both the buyer and seller.

I sold some coins on Ebay (gold bullion). I sold a few more then I had on accident... this is how I was in that position. Not because Im a scammer.