No, I’m not suggesting the shop intentionally contaminated the sample at all. I’m only pointing out that if the gasoline was bad enough to require a tank drain and flush along with a filter replacement (you previously stated pump, not filter) then the car should have been exhibiting symptoms shortly after you filled it up; as in a few minutes.
Your car would not even have started to make it 12 full miles on the fuel in the lines. Just an FYI here, but the fuel system has a return line to the tank and the fuel that is pumped from the tank to the engine makes a round trip back to the tank.
This is occurring constantly while the engine is running.
Any “good” gasoline in the lines would be purged back to the tank and replaced by the alleged “bad” gasoline in a minute.
Now that you’ve stated you have a sample, what does this sample look like?
Does it have a normal gasoline smell?
If you suspect this gasoline is not up to par so to speak, then try this.
Go out on the driveway and pour a tablespoon or so on the pavement. Quickly cap and set the jar out of the way. Throw a match on the small puddle of gasoline.
If it goes up in a flame quickly the gas is fine; if it is slow to ignite or appears to burn slowly then there could be something wrong with it.
The part I’m having a lot of trouble with here is reconciling gas so bad that it kills a car but yet you managed 12 miles and 3 trouble free trips on it.