Let's also keep in mind, the original question was not whether we can or should trust someone to send a check, but whether a seller must extend that trust - I would hate to be in the position of the seller in your original post who had reached a $500 deal and then saw it cancelled because the two could not reach agreement on the sequence of shipment and payment. Perhaps this would have been a time for an intermediary to be used to assure that goods and payment were both delivered.