This is so 100% correct. From my experience (simple SaaS) it is like this: 1) There is about 5% to 8% of customers who might be very hostile at very beginning

This is so 100% correct. From my experience (simple SaaS) it is like this: 1) There is about 5% to 8% of customers who might be very hostile at very beginning of interaction 2) However, 60% to 80% of these people can be calm down with a few nice words. Put yourself in their shoes - it might be something else completely unrelated to your product or service made them angry. 3) If the above does not help, we politely close conversation and fire the customer so that we can focus on other customers. Easy for us. The problem is that it is much much harder do "fire customer" if you are a flight attended, if you are teacher, cop, etc. For example, I just had a parent-teacher conference and my son's teacher was crying because the parent before me was one of "unreasonable ones". Next time, I bet the teacher will just call the police so he does not need to talk with that parent any more. So this is a conundrum... 3% of pathological customers will make us all suffer.