To the OP, whatever action you decide to take in a situation, do it decidedly and don't "what if" yourself to death (literally). Rely on your training and preparation to guide you in the right course of action. There simply isn't time for "what ifs" when someone is closing ground.
I will add that I try to scan gas stations as I'm pulling up to a pump (or parking lots or whatever) and before I get out of the vehicle. There have been a number of times I didn't like what I saw and moved on to the next station or parking spot.