The phrase "I've got a bridge to sell you" comes to mind... I don't think the buyer would be in any particular legal risk. The right question to ask is "will I be able to get a refund after falling for this obviously fraudulent / mistaken listing."

An organization like facebook doesn't go down in a day. The domain name (and, presumably, associated trademarks) would almost certainly be auctioned off in a highly publicized event.