This article with comments was terrific - it was so informative. I found the advice useful. It addressed specifics like the condition of the dry wall surfaces, any additional repairs such. pin holes, chalking, smoothing of wall surfaces, absorption of paint and number of coats that may be needed. It should also include insurance coverage, and reflect the clean-up afterwards. Having a written contract with the company's letterhead is a must.
Maybe you've just moved into a new home, and you haven't got around to buying brushes and rollers yet. Perhaps you're worried that your brush-skills aren't that good, and you won't achieve that professional-looking finish that you’re really going for. Handy professionals will turn up with everything they need to get the job done, from ladders and brushes, to rollers and tarps. You just have to provide the interior paint and primer!