This happened years ago but I still think about it. I always went to this gas station in my town, and it was usually pretty busy. Whenever I would go to any gas station, I would go inside, prepay with a twenty dollar bill, and then pump my gas. At every gas station I've been to, the pump shuts off when it hits the prepaid amount, and this gas station was no exception.

But one day when I was pumping my twenty dollars worth of gas, I noticed that the pump didn't shut off. I had prepaid with a twenty dollar bill just like all the times before, but this time it filled up my tank and I got maybe about 8 dollars worth of extra gas. I thought the pump malfunctioned, or the cashier didn't input my prepaid balance properly.

Either way it wasn't my fault and I thought it was my lucky day, like getting an extra soda from a vending machine. I was about to drive off, but then the cashier came running out saying I had to pay. I explained to him that I prepaid with a twenty dollar bill, and it wasn't my fault that the pump didn't shut off like it was supposed to. I didn't want to pay any more than twenty dollars, which I feel is the whole point of prepaying.

It definitely wasn't worth arguing over, and I did get the extra gas, so I just paid him and that was that. I didn't go back to that gas station though. But I'm still wondering, was I obligated to pay? Am I ignorant on gas station etiquette?