After owning a dealership and working at a dealer and managing a dealership. I have had mechanics that had very few mistakes or almost no mistakes. Then there were the ones that I fired usually not soon enough.  Having the right person is the first thing. Then having someone look over and inspect the job is very important. I did a lot of that ask questions, have quick talk with the mechanic about what was done how it went. And even then, sometimes thigs happen. And I all ways did my best to make it right if we screwed up.