Depends where you live. I live in Australia, and there isn't a single service station that makes you prepay where I love. You can just pump and pay at the end, always.

It's possible that some of the places that used to skip prepay were illegally taking the cost of a pump and run out of the pay of whoever was on register. I've never experienced it personally, but I've heard a lot of stories.

In my wanderings around the USA I've only encountered one pump that allowed pump before pay. At some obscure Nevada gas station in a little pass-through town in the middle of nowhere.