1. Look up the license
Ask for the company's Oregon Construction Contractors Board (CCB) license number and look it up on the state CCB website. The CCB says contractors with an active license are required to carry a bond and insurance. Check that the license is active and that the business name matches.
2. Ask for proof of insurance
Get a certificate of insurance, not just a verbal yes. Roofs and ladders are where things go wrong.
3. Ask how they remove moss
You want a low-pressure treatment and brushing or blowing, not high-pressure blasting of asphalt shingles. Ask what product is used and how runoff near plants and drains is handled. Ask whether any licensing applies to the products they apply; you can also confirm requirements with the Oregon Department of Agriculture.
4. Get the scope in writing
The quote should say what is included: moss, algae, gutters, downspouts, any preventive step, and cleanup.
5. Get the guarantee in writing
If a company promises no regrowth for a number of years, that should be written down with its conditions.
6. Beware of up-front payment and pressure
A large deposit, a same-day-only price or a refusal to describe the work are all reasons to walk away.