The probems are many. Fuel is fuel and just because you bought it at joeschmoes gas station does not make it different from the place across the street. When local fuel distributors purchase bulk fuel, they only differentiating factor is the additives that they then put into the fuel. New federal laws mandate different fuel characteristics for different areas of the country for different times of the year.
Most fuel now has alcohol in it to raise the octane rating. Areas of high concentrations of population have "reformulated", oxygenated fuel, which burns "cleaner." Look at the dispensers and the redesigned nozzles in the city.

Because the pickup tube for an in-ground tank is three to five inches from the bottom of the tank, many (read MANY!) fuel stations fill the tanks with two to four inches of water. They do this so that their money is not "wasted" on fuel that they can never sell. They put water finding paste on a stick and measure to maximize the water benefit.

I have seen the people dump five gallon buckets of alcohol at a time to the tanks when they put too much water in.