Some buyers wait for receiving miners and switch it with broken machines. They keep the miners and get the refund from the escrow. Sellers need to find a way to mark their miners.
Life with crypto....Otherwise go to ebay I say...if every newbie just came here and asked for $10s of thousand of dollars from someone anonymously with a payment that is irreversible there would be noare here. Escrow and escrow only allows for us to transact in bitcoin...