130+ transactions, all but one went fine, seller never sent item. I'd always recommend that you disclose up front any issues, cosmetic, functional, quirks, otherwise, it'll come back to haunt you. People seem to want prisitine collectible cosmetic items, when they are buying used, so I always under-rate the condition. Better to be conservative IMO.
If buying, ask questions, are you the original owner, does it come with the original box, are there any issues, quirks, has the item ever been repaired? if so, by whom.
Nothing that doesn't fall into common sense either in buying or selling.
IME, audiogon buyers and sellers are way nicer to deal with than eBayers.