This all comes down to the rules.....1. references....does the contractor have them??? I ALWAYS furnish all my prospective customers them....no excuses...2. insurance....again, I always furnish proof....3. Read the proposal carefully...I ALWAYS list materials down to tape used, the brand, the grit of sandpaper, the manufacturer, etc....its INEXCUSABLE to not list all of these items....I am a member of the PDCA, the Painting and Decorating Contractors of America, the foremost authority in the coatings industry and they also approve of what I listed....if you do not follow these guidelines, you will NOT get a job reflective of "professional". Look for the PDCA where any painting contractors are, if they are not a member, RUN!
In some cases, professional painters may include additional charges for specialized equipment that homeowners can't purchase on their own. Because professionals have licenses and access to such equipment, it's simpler to let them get those themselves. But providing some of the smaller equipment and extras directly really can help to cut down on the total cost of your project.
Recently I had the outside of my home painted. The contractor wrote a good contract, but I failed to realize that some things were not in it. It reminds me of the car dealer who offered a good price on a new car but failed to mention that it did not include tires. My contractor failed to specify that lattice under a porch was included. So the painters did not paint it. To his credit, he did instruct them to paint it when I brought it to his attention. If I had the job to do over again I would look for an individual who came with referrals from happy customers rather than a franchise owner..