One definition of professionalism is consistency of the desired result.
Some vendors achieve this and some don't which means on some actions it works out fine even though you are dealing with a seller that is not top notch.
I try to place my business with professionals as I like the odds of a good result when I order. With such people, I consider a mistake to be a fluke and not SOP.
I am sure everyone has some different experiences with any vendor depending on what and how often they order.