#15 The Very Lucky Vending Machine
I found a vending machine at work that didn’t differentiate between quarters and golden dollar coins when dispensing change; when it was supposed to give you quarters about half of them were golden dollars. I put in as many $5 bills as possible and bought the cheapest item available and got ~$8 of change back each time. My total profit off that machine was over $50 before it ran out of golden dollars.
Credit: Justwantedtono