It probably boils down to the body work. I can't and don't want to do it. Maybe there is someone somewhere that would do it and then I paint. But it does not seem like anyone does it that way. The painter, or their employees, do it as part of the "job". Maybe that's a business opportunity....PaintPrep, Inc. That's what I need. So we are round and round again. That's why Maaco is in business so long.
The money is in the body work. 50 hrs of body work and 2 hrs to paint....+ paint and supplies. (estimate hrs just to make a point, ratio may be off)
So you have a painter who adds that all up and charges you per hr. Spells it out. That's fair.
Then there is the guy who adds it all up and adds a profit on top. All figured in his head, after looking you over. That's fare.