You need to keep in mind what type of paint is on the car. In the days when lacquer was popular it would not be un heard of for a car to 10 or more base coats and just as many coats of clear. Lacquer would orange peel like crazy and you would wet sand off as much as you left on the car.
With modern paints the base coat is very thin. The base coats plus the clear coat combined is about as thick as a single stage paint job. In my opinion if the factory paint is good shape it's ok put down an epoxy primer or sealer and repaint it. If the car has already been repainted it's best to sand it off before repainting.