Hey Dan,
There's been a couple times over the years I've gotten really good deals on ebay auctions, paid promptly, and then received a message from seller stating he "mistakenly" listed the card but realized he had previously sold it. (And yes, the same seller put the same card back up for auction a few weeks later!) I think this sort of thing is quite unethical, but I typically just take the refund and take my business elsewhere. Life's too short to get panties in a bind over these things
Best regards and happy collecting
Craig