In some petrol stations scammers can "swap pumps", so they fill up with your money! It turns out some pumps can be swapped at the base and a criss-cross of nozzles take place.
The unsuspecting driver picks up the non-functioning pump, and thinks they are filling up, but it is their neighbour that's really filling up at their expense.
Most people would know straight away that something was up, there would be no pressure on the pump, but in this season of office parties, hectic schedules, and general overdoing it, it is easy to miss.
Make sure you get what you pay for.
Don't kick yourself later, just give the pump a quick once over before you pump!