I would like to address this subject from the viewpoint of having had a career in the car repair industry, not only as a mechanic, but as a service writer and service manager as well.
A bit about me, I studied auto repair in high school, as well as acquiring an AA degree in auto mechanics in college. I then went on to work in a car repair shop on an air force base in Sacramento California. For the next several years, I worked as a mechanic at Datsun dealerships (which later became Nissan) in California where I was sent to factory schools for more specialized training on the Nissan vehicles themselves, which training courses over the years covered various different areas of the vehicle. At one point, I decided to open my own garage, which I ran for many years. And then on to creating a used car dealership which then evolved into helping charities increase their funding by turning donated vehicles into cash.
Back to the subject of choosing a repair shop. When I started in the first dealership the mechanics were paid by the hour. Overall we had a great group of guys. That dealership ended up closing down, so I migrated to a different Nissan dealership, but this time the mechanics were paid on commission. What I observed was a bit shocking for me, with some of the mechanics being money motivated rather than service oriented like I was used to. That was when I soon decided to start my own repair business.
Inside a repair shop, you have varying degrees of skill, training, knowledge, intelligence, as well as ethics, depending on which mechanic is given your car to work on. Sometimes you might get a trainee, other times you might be lucky enough to get an expert. Or you might be the unfortunate one to get a crook working on your car, I have seen it happen many times.
Often times, a real expert mechanic may decide to open his own shop and specialize in a particular make that he has experience with. This is the kind of person you want servicing your vehicle, where you have more control over who works on your car. Plus these kinds of shops are normally small where the owner can maintain tight control.
So in looking for your next mechanic, I highly recommend you look for an independent shop that specializes in the make of vehicle you own and who is factory trained. And with good reviews of course.
But when it is finally time to replace your vehicle, remember that you can always donate it and pay less income tax and get the satisfaction of helping others.