To paint a large section without leaving lap marks, roll the nearly dry roller in different directions along the dry edge, feathering out the paint as you go. After completing the entire length of the wall or ceiling, move to the next section and paint over the feathered edges. For the second coat, apply the paint in the opposite direction. This crisscrossing paint application sharply reduces (if not eliminates) lap marks.
More recently, professional painters are responsible for all preparation prior to painting. All scraping, sanding, wallpaper removal, caulking, drywall or wood repair, patching, stain removal, filling nail holes or any defects with plaster or putty, cleaning, taping, preparation and priming are considered to be done by the professional contracted painter.