Way back when I was in college, I had a classmate that worked for a car stereo shop.
The way that owner ran the shop, the guys in the showroom were responsible for "reading" the customer, to see who was on the ball. The guys in the installation shop were trained that if a customer work order came through with "CC" in the top corner, that meant Cut Corners.
In any era, there have been sleazy businesses. Sometimes I think that has only got worse with time, but that isn't really why I'm typing right now.
As hard as you studied in school, some of the tougher lessons come in the Workplace. IMO, a lot comes down to what I call The Game, or the Unofficial Rules of Engagement.
In some shops, the Shop Supervisor gets paid on Hours Booked, # of Jobs (allegedly) completed, or other expressions that come down to Volume of Work Produced. If Quality has to suffer, so be it. In many cases, outright fraud is expected.
Those aren't the shops that I want anything to do with, either as an employee or a customer.
The hard part about The Game is learning (had to get a few of those T shirts myself) that until you set up a business with Your Name over the door, you can't really change The Game. As people have already stated in other ways..... You either (1) Play The Game their way, or (2) You Leave.
Part of the homework in evaluating a future place of work is determining how they Play the Game. The trick is finding the shops where your goal of Quality Work with Zero Call Backs is a good fit.
BTW, this affects all industries, be it fixing machinery, building houses, writing software, whatever.... the human factors are pretty constant.
Part of the research is just talking to everybody you come across. Staying with the Ag theme, asking a long time farmer what they think of so-and-so equipment dealership is always a good idea, and be open about it - say you are looking for work, and want to find a shop with a reputation for taking care of their customers well.
You've had a few conversations that have already turned into short term business. I'll wish you Good Luck, but I don't think you'll need much - a conscientious mechanic that is willing to work won't be idle for long.
Move on to your new activities, but never lose sight of The Game. That was just Round 1.
Rgds, D.