I don't think it's just the "twat" factor. You can only do so many "I haven't received the goods, refund my money" before you accumulate such a horrendous feedback that nobody will do business with you again. In addition there is a chance your paypal/ebay accounts can get shut down.
You exchange positive feedback before you send the refund request. And sellers can't leave negative feedback any more.
With that said, your ebay account might get shut down after this happens more than a handful of times. Better pick up some spare accounts from a botnet operator.
