I would ask Ebay to remove the Negative Feedback. Since you won the claim the guy put against you, you might have a chance. It is worth a shot.

I have sold pathtag tokens on ebay alot and for a long time just shipped them in envelopes like I would a trade with someone. Free shipping or 50 cents just to cover the stamp. THEN one person decided that he wanted a second set of tags. Claimed he didn't get them (even though he logged on the pathtag site that he had a set). Well, I refunded the money instead of shipping another set. then I raised my shipping to $2.50 and ship in bubble mailer with dilivery confirmation. I put in the description that the reason for the high postage is due to an ebayer claiming a package never arrived on every auction. The person has never bid on another one of my auctions.