Back in my days in consumer car repair, I worked at a Dealership and some independent shops. What affected my ability to repair in all cases, and what prompted my moving from one business to another, and led ultimately to my leaving the profession, was corrupt management that expected me to also be corrupt.
Basically I was told to find things to repair, that really didn't need to be repaired. Then explain to the customer why the bogus repair was absolutely critical, etc. I think the profession has improved in that regard, mainly due to numerous undercover stings by news organizations looking to expose the then rampant fraud.
About 15 years ago I started working in professional racing as a hobby. You absolutely have to do things correctly as there is no margin for error, AND you have to be fast. You're also away from home for most of the year. People enthusiastically join up, but then it becomes clear they lack the skill, the speed, and/or just the desire to be away from home for extended periods. Very few make the cut.