So, was that sale local? The buyer came in and received item after handed you cash for it?. This would mean the buyer had an opportunity to physically examine the item which "appeared" to be in working order and as described in your auction.
If you have in your item description "no returns" than I think you should win if buyer complains to Ebay. This was not PP transaction, so I wouldn't worry too much as PP is known to side with buyers all the time
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