Yes Barry, and their customers can tell them where it hurts! And even then, they quite often misdiagnose!
Seriously, though, the problem is not one of competence, it's a simple lack of quality control by garage management. Even a highly skilled tech with a high level of training can overlook items, though hopefully, not as many as seem to have been overlooked here!
Sloppiness has no place on the road or in the workshop, good working practices would eliminate these problems.Good management and supervision are essential. Spot checks on Technicians,fully detailed check lists issued for each type/ model to each tech, and one guy doing spot checks on each vehicle before it leaves the workshop.
Every vehicle should be treated as if it was a Which? car. Which? is how it should be!!