In my whole life I have found the VAST majority of mechanics are fair and proud of their work and expertise. There certainly are exeptions and there is incompetancy or mal-intent out there but that can happen in any situation.
In defense of the mechanics out there folks should know how difficult and expensive it is to even be in the trade. There are a lot of dissatisfied consumers and some of that is justified. Where I live and work rust and corrosion is a big deal. An easy job can be a nightmare and take hours to correct a broken fastener. Things that fasten exhaust parts and the flare nut type fittings used in brakes, fuel lines, transmission cooling lines, power steering lines and more are a wicked pest and if they cross thread a new part can be rendered junk and it takes real finesse not to allow that but most of us have had that happen and know to avoid that at all costs. If that happens to a new part it would be mechanic error and the part warranty would not cover that. If something like that happened the mechanic should take responsibility for the costs for that. If they own the shop and did that they pay for that. If they are employed at a shop and make that error the shop pays for it and mechanics works for free to correct it. Shop owners will tolerate some of that but not for long as the time spent on a redo is a waste of time which is money for the shop.
It behooves the shop to fix the problem and maintain their reputation which totally pays off with happy customers who near always will tell friends of the good experience.
It's a hard way to make a living. You end your day dirty, smelling of car odors, get cut, burned and risk getting hurt almost every day!
I find the root of most problems is lack of communication. Did you get what you asked for? Did the mechanic understand your specific needs or limits with the cost of the work?
No one wins when things go wrong,
T