Reply to #3:  does is stop after 2? if you were to hold the plate when the second product fell, would you be able to get your money back a second time?

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great trick...

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It works like this: the output of the machine is locked by a mechanic plate which moves to release the product after it's bought.
You can fool the machine by holding the plate when you buy the product. The product falls on the plate but you can't get it because it lies on the plate that you are holding. Then you request your change back. The machine will assume that it hasn't served the product, because it did not release the lock. Now you can buy a second product. This time don't hold the plate, and you get 2 for the price of 1.

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please, explain it better. I don't get it

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i don't get it...

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