Ethanol gas is garbage, so there you have it, it's all bad for the most part. I only use non-ethanol.
I personally have never heard of anyone getting "bad gas", accidentally putting diesel in a gasoline powered car, that I've heard of. I worked at a gas station and we checked for water in the holding tanks every morning. Sounds like some folks were getting gas from less than reputable station owners. Oh, if your car pings, especially back in the day, your timing is off. Had nothing to do with the quality of the gas as much as piss poor maintenance. I never had a car ping, but I own and know how to use a timing light and dwell meter.