Admittedly, I've only had rare cases of bad gas. Once was from Husky/Mohawk in the Audi, which was odd because I have bought there very regularly without problems. I guess one bad load in over twenty years isn't a big deal. The discount stations have given problems, too. That bothered me the most, though, since it was with the fleet, and those vehicles were not terribly fuel sensitive, so there was obviously something terribly wrong with the gas. Stock Chevy 305s should not be pinging like mad in urban traffic on regular gas.
Another piece of anecdotal evidence (and nothing more than that) is a First Nations lady I know up here who refuses to fill her new vehicles on the reserve (which has a new station), even though she could get the gas substantially cheaper there due to the tax breaks. Instead, she buys the gas from regular stations, paying a hefty premium. She claims that her vehicles run poorly on the off brand gasoline.
Personally, I avoid the really, really old stations that haven't had tank upgrades for a number of years, even if they are Top Tier. Coops are good here, too, since there are plenty of new stations. I tend to go to Petro-Canada the most, though.
