Casa- years ago I was trying to figure out why my motor ran crappy once in a while. I eliminated one thing at a time and finally I isolated the problem. This also goes for my other small engines (weed eater, lawn mower, etc)
It was the gas bought at a particular gas station. The station was not a high volume place and it was kind of run down, but convenient. When I poured some gas into a glass jar- it was cloudy and lots of particles floating in it.
So I took it all and dumped it in the truck and burned it up. Did not notice any difference in the way the truck ran.
Bottom line to me - if the owner let's his store fall in disrepair, he certainly does not care about the condition of his storage tanks. His business model is to buy the cheapest he can and sell at above prevailing prices and his store is nearly always empty.
I stay away from these place as I remember my aggravation.