As was said, the two most essential qualities are honesty and mechanical knowledge
These are probably the MOST essential qualities. My wifes 96 Accord had a recall to replace the cam seals. Since the car was due for a timing belt change when I set up the appointment for the cam seal I inquired how much EXTRA they’d charge to replace the belt. Service Managers response…“Same price with or without the cam seal.” I said why’s that?? Since you have to remove the belt to get to the cam seal. His response “We have this special tool so you don’t have to remove the timing belt.” WHAT AN IDIOT.
When I dropped the car off two weeks later…he was dumbfounded why I didn’t want them to replace the timing belt.