Might already have been mentioned, but do engineers use checklists?
I ask this because many years ago I innocently asked an engineer the same question, as his hands were flying all over the overhead panel, while we waited to close up on stand. (BAe 146). "No he said, we use common sense".
It strikes me that a hard pressed engineer could conceivably make a mistake*, and giving the trim a twirl, sees the trim tab moving and 'confirms' that it is connected and working correctly. But crucially, it might be rigged in the opposite sense. Ditto primary flight controls. Working on many different types, it could be possible to make a mistake. Or a junior engineer, asked to confirm movement might confirm correct movement but not actually be 100% sure about the direction.
Likewise on a control check, the correct direction of movement of the flight controls needs to be positively confirmed, not just that they move freely. Several times, during control checks, the PM has said "full left" when I was holding full right. (Airbus - where you can't easily see the other pilots side-stick to sub-consciously 'cheat' in the control check).
It would be comforting to know that engineers would use a check list after work on flight controls, that specified for example; ' move the XX trim wheel in YY direction, and confirm the trim tab moves up'.
*We all make mistakes - I've made some howlers - and I mean no disrespect to any engineers.