Adrian, I'm shocked to hear the mirror story.
Painting door properly is not easy. It requires removal of upper rubber/chrome strip (you need to remove the upper door frame with glass), handle, rubbing strip and lower plastic strip. Basically, complete door should be stripped to be painted without compromises. This is how door should look like before painting:
I'd never allow others to disassemble the door as these people are time bound (which means no quality) and they genuinely don't care what will happen with your car in future as we learned with the mirror.
[Rant on]
Sometimes I hate this commercial capitalism paradigm, which is not aligned at all with my interest of car owner. People are **completely** not interested to deliver uncompromised highest quality. Cut corners everywhere and use cheapest stuff to maximise their margins.
There are 3 islands of dedication to quality on planet Earth where we can still find some remains of decent quality and long term approach: Switzerland, Germany and Japan. No UK in this list
[Rant off]