Actually aircraft work is not nit-picky, the manuals leave a lot to desire in many cases. More people get into trouble over paperwork than how they did something. There are bad apples and don't care if they do a job right, or even just pencil whip things (like lubes). But for the most part people try. And mistakes do happen. But most get caught by inspection process or just others looking things over. Things do get missed. And the general public has no clue that a plane they are on could have dozens of things not working. And there is a process to defer some items. Every plane (airliner) has a Minimum Equipment List. And that basically tells you if the plane can be dispatched with something not working. There is no limits to MEL's on a plane. There could be 50 things or more deferred as long as the manual says they can be inoperative. And that's what mechanics are doing while the plane is boarding, and you hear a pa announcement, we are finishing up some maintenance paperwork, and yet you never saw a mechanic touch anything on the plane while it was at the gate. Unless it was something simple like a light bulb in the cockpit, there is no time between flights to fix much of anything.