Ive had this idea in my head it is quite similar to what you guys are thinking kinda
welll there could be some kind of sign when you say buy item # that says what your buying how much its put up for and it also asks you a secondary check to see if you want to buy it so some one dosent like put a apple up for 500 and goes under the item and holds up a rare hat and if you fall for buying it you can cancel the your buying if you see that its a apple on the sign
it would be a great way to stop that scamming