Vending machine that would buy a item, you would have to put item which you want to buy, and for what price do you want to buy it. People who have that item could come and sell it for the price set in the vending machine. If the item would cost 40 wls and there would be 80 wls in the machine, 2 would be bought, if there would be 40, 1 would be bought. Or the owner of the vending machine could just set how much items he would want to buy.