There are so many parallels with what you folks describe and what I do professionally.
I remember how badly I felt when I had just completed my fellowship and had a patient request records to be sent to another physician. I work hard to go the extra mile in explaining things to patients, trying to be kind and gentle in delivering bad news...and I remember doing significant introspection. And now...many moons later...I recognize that I can't solve everyone's problems, that I can only do my best and that I treat my patients as I would want my family members treated. I still think it to be important to be introspective, especially now that my "give a **** (GAS)" level is exceedingly low. Throw into that mix the internet, which makes everyone an expert, and my GAS level goes even lower.
It is equally difficult for patients/clients to know how to assess a doc/mechanic. Not all docs are the same, not all mechanics are the same. How are our clients making that decision? Many use online reviews to help with the decision, a few rely on recommendations from their physician, many others use recommendations from their friends or coworkers. I like the latter, as usually birds of a feather flock together and if their friend had a good experience with my care it is likely that we enjoyed caring for them...and will enjoy these patients, too.
When I see someone for a second opinion, or I see that they have gone to more than one doc for their care for this problem I wait to see how my first interaction goes with them. Many times these people have gotten suboptimal care from others and I know we can do better. They are very frustrated, and I often can understand why. Occasionally the patient starts off bad mouthing the previous doc and I have to make a decision as to if there is good reason for this, or is this just an unhappy person. If I suspect the latter my GAS level helps me end things sooner than later. It is important, though, to know that prospective patients, and your prospective clients, are in a tough spot.
With mechanics, there isn't Yelp or other online resources available to prospective customers, and to make matters worse it is not often that the choices people have are limited at any specific airport. It may require us to fly out of our airport (where there is a suboptimal mechanic) to one many miles away to "get the job done right". The average aircraft owner isn't likely able to know what "done right" means.
I do think that for you guys and me life is too short to work with intolerable people. It is likely that if you have problems with a person it is likely that others have problems with that person and it is much easier for all involved to disengage. When it reaches that point for me and a patient I arrange for a free "Come to Jesus" talk, so I can "splain things" to the patient that I am unable to meet their expectations, and that they either adjust their expectations or they go to someone who can meet their needs. It may not be me, and I am OK with that now that I am an old doc.
...for what its worth.
Randy