I notice that most bad service experiences end with "And I'm never going back there no matter what". (Or never using their service, never ordering from them again, etc.)
What is everyone's threshhold of "never returning"? One bad service incident? Two?
I tend to not vow not to return until I get bad service at least twice. I also try to take a mental average. If somewhere that otherwise does great work has a couple of bad visits, I'll give them more of a chance to redeem themselves.