[header] How to hack a candy machine [title] Put double stick tape on the coin. [step] Use strong double stick tape to attach the coin to the knob. If the tape is strong enough, the coin won't drop or be pulled off as intended, so it can be reused for multiple pieces of candy. 
[title] Try turning the knob back and forth. [step] This will only work on a low-quality machine or a machine that has not been properly put together, so just try this once and move on if it doesn't work.