A true professional understands that it is his or her responsibility to provide a quality job for the homeowner. Professionals also know that attention to detail is a part of the job. While a homeowner might leave a bit of paint on the window pane, a dedicated interior painter for hire will make sure that these small details are handled properly, because a perfect job is the best calling card.
Consider purchasing supplies personally to save money. Ask the painter for a bid that separates labor and materials. Then explain that you'll purchase the materials and ask for a list of exactly what will be needed to complete the job. Caulking, for example, is an extra supply commonly used to fill any cracks or damaged areas in your walls -- and one that might be overlooked in an incomplete list.
Here is where this affects you as a consumer. You select a painter with a contract that says 2 coats, $500 down. You give the company the deposit and pick your colors a couple of days before the project starts. The painter goes to the store with your colors and figures out they are deep base. He (or she) not only needs to charge you more for the paint, but he also needs to charge you for a dark gray primer coat. Ninety nine percent of the time that primer coat is going to be really, really expensive since you already gave a deposit.