Leave him negative feedback. If the transaction sucked, say so. Let him leave negative for you if it makes him feel better. If you have a good record, nobody is gonna care.
Then forward to eBay, but if the seller is a powerseller or they make alot off him in fees I wouldnt expect anything more than an empty promise to investigate from them. They usually wont do anything to sellers except in cases of clearcut fraud or when there are *alot* of complaints about a given seller.