Unless you like textured walls, don't paint over dust. Wash the walls with trisodium phosphate (TSP) or a mild cleaner, like Jasco's TSP No-Rinse Substitute. For smoke-stained walls, Toto uses a 50/50 solution of bleach and water. To clean a wall, use two buckets. Load up your rag or sponge from your cleaning-solution bucket, and scrub. Before redipping, rinse the sponge in a second bucket filled with clean water.
As a former professional painter, something that drives me crazy is when I see painters cut in around wall plates. First of all, the amount of time that it takes to cut in is usually much longer than the amount of time that it takes to simply remove the wall plate. Secondly it does not look nearly as clean as it does when the wall plate is removed and thirdly it can invariably leave paint on the wall plate itself which also looks sloppy. Make sure the painter takes them off and then reinstalls them. It's less time.