The vending machines in our building are equipted with the GOLDEN EYE and the machine looks like this:
The golden eye gurantees that you get the product you purchased and if you don't get it (the eye doesn't see it fall) it will continue two more tries to deliver the product and then refund the money or let you make a new selection. This is an ingenious idea. what better way to keep morons from encouraging a 400+ pound machine to fall on them because it won't give them what they payed for.
I have heard rumors that some have tried to 'blind the eye' with a laser in hopes it would continue to dispence product (much like some slot machine hacks I've heard of) but alas, it is rumored to have not worked. If I were to design this I would pulse data on the golden eye so they eye could not be faked. how would you build it?
Since it will keep trying to dispence product until it sees something fall it often results in multiple items being dispenced from a single purchase.
method1: item falls and nocks something loose below it
method2: an item gets hung up, so the machine keeps turning the screw, then two products fall from a single purchase.
This gambling addition was a very good side effect. I have personally witnessed people buy more than they normally would because they want to take the risk to see if they can 'cheat the system with a two-for'. in the end, they sell more product and I'm sure it offsets the minor loss they incur for the doubles payed out. either someone was really thinking when they designed this or they got lucky.