I guess the toughest thing to get across to a prep DIYer is that any scratch, any dent, any hump will be visible in the final finish. Some folks will then complain about those defects, as if the paint would fix them somehow, when more often than not the paint amplifies the problem.
The trick about body and prep work is in the eye and the hand. When you do it daily, you see and feel the problems. When you dont do it daily...
The comments above about incompatible primer is on the money.
The thing about folks bringing in a bucket of paint is the fact that the painter may not be familiar with the material. This puts the painter at a distinct disadvantage. Bring in the wrong reducer for the temperature/painters style, more problems, and all of them have to be solved on the fly.
Me, I paint modern base/clear on modern cars. Hand me enamel or lacquer, I'm out of my comfort zone.
As far as what a job would cost, that is going to vary widely by location.
OBT, you might check with a MAACO or Earl Sheib paint job. Might even snag a painter to shoot your truck for you "on the side".
