A good friend of mine is a weights and measures inspector for the government -- he goes around and checks the accuracy of gas pumps. Look for the little inspection sticker. If it's up to date, most likely this isn't a problem. According to him, this kind of thing is really rare, and happens mostly with older pumps, but not because of fraud.

Other friends of mine use to operate a gas stations. Gas station owners are small business franchises. They're not the big oil companies who are making the huge profits. They only make a few cents per gallon no matter what the price is.
_________________________
http://dcvance.wordpress.com/