example for regulation

If I own a gas station, I sell 3 grades of gas for 3 different prices.  One day per week, I could switch the tanks and sell 87 octane at the 93 octane price, and no one would ever know.  If I can get away with it, shouldn't I?  Is this someplace where the government could regulate and try to prevent this sort of fraud from occurring?  Or should we all have to test all the products we buy ourselves to ensure their purity?