As much as I am confident many pump operators out there would do anything to make a quick buck at the customer's expense, all it takes is one time metering more

As much as I am confident many pump operators out there would do anything to make a quick buck at the customer's expense, all it takes is one time metering more gas into your tank than what your tank is able to hold, after which you know they're lying and regulators will get involved. Even if not, word of that kind of thing spreads and it won't be long before that filling station's competition starts stealing its business through word-of-mouth.