A thorough scrubbing is a must before painting any exterior surface. It removes the dirt and broken-down paint residues that keep fresh coats from adhering and gets rid of mildew that grows on paint in all but the most arid climates. Most contractors clean with pressure washers, but in the hands of someone unfamiliar with the equipment, these can gouge wood, shatter glass, and drive water behind siding and trim. Using a hose, a pump sprayer, and a scrub brush is slower but safer, and just as effective.
The other difficult part is getting a painting contractor to show up. While this generalization does not apply to every painter, you can rarely get a paint contractor to show up to look at the house and to later produce a written estimate. It's hardly the fault of the painting contractors; it is a combination of the contractors being smaller operations along with a high demand for their work. House Painting Arvada