If it was delivered then the sale is final. There is nothing the buyer can do about it. He can file a claim and you can dispute it. There is nothing more that can happen though. I also agree with what Hilary said. Every time I put an item up for sale get lowballed by a member on items already priced very low and then he claims he wants the item and schedules a time to meet and NEVER shows. Needless to say I refuse to deal with this person now. I'm a nice guy and people who have bought from me get what was described and in some cases more. I've probably given more away than I've sold as I don't sell very often on here. But you can't satisfy everyone and it's useless to try.
Lately, some members have been less than pleasant to deal with in the FS threads. I keep everything as simple as I can. No holding, no shipping and no paypal. Cash only and first come first serve.