In my experience, inexperienced mechanics don't have a good feel for how tight a bolt should be. I have a young engineer working for me, great guy, smart and capable. But he doesn't know how tight a bolt should be. I have to go behind him and actually tighten everything.
Of course that can go the other way and there's plenty of newbies who strip fasteners. Weve all been there.
I worked in a transmission shop as a teen. We had a Mercedes in and the boss cautioned me on the install to be very careful about stripping threads on the bell-housing. Guess who stripped a thread on the bell-housing? Guess who was out of a job a few weeks later? LOL