Speaking strictly from an insurance point, KTAC has recovered several stolen units because someone got a "good deal" on a stolen unit and later tried to get it repaired (and found out it was stolen). Once an insurance company pays for a theft claim, the equipment belongs to the insurance company. Unless you check the serial number against the national database (for stolen equipment), you can't be sure if the seller is the owner. The sorry part about this type of transaction is the buyer isn't protected against consumer protection laws (at least thats been the case so far) since the seller is not a business. The buyer is out the money and has no equipment to show for it.
I am not saying this is a scam just saying protect yourself against it.