I've Tried the Convener hack, the one where you block up the door to get a free soda, but it NEVER gave me the refund! Instead I had to pay DOUBLE just to get the original and a secondary drink.
My next trick to test, is the tape on the dollar. I tried it before without complete coverage, and cheap ass tape, but it just ripped the dollar up and horribly mutilated the machine (3 feet of sticky tape coming out of the dollar slot) I am going to try again with packing tape, that has a diameter almost equivelent to a dollar, so I get complete coverage, and no paper that can rip. I wonder If they have installed cutting mechanisms to stop this kind of hack...