I discovered this myself

if the machine looks like this:


you can get more than one drink out of it for the price of 1. You see, after the machine processes your order the drink will fall onto a arm which will then raise up so that the drink can slide out into a slot for you to take it. What you have to do is hold the flap shut so that the drink cannot enter the slot and the machine thinks it has not vended. Press the button for money return and get ur money back. Repeat until the arm has on it as many drinks as u want. Carefull though, if you try to overload the arm not all drinks will fall out. This is a great way of ripping off machines.