Once you are on the Washington State L & I page of a contractor (see Verifying a Contractor Part 2) look around at some of the sections. There is a wealth of information there.
Notice the section Lawsuits against the bond or savings. Here you can see if the company is a repeat offender for getting sued by sub contractors, suppliers and others. Do the obvious. Stay away from bad actors.
Look at L&I tax debts. A business that can't pay taxes on time is not likely to do a good job for you.
Look at License Violations. This is often things like employing unqualified labor, failing to maintain a safe work place and other non-compliance items. Cutting corners on these items may mean a lower price to the customer but often at the expensive of quality and reliability.
Review the item Estimated workers reported. If they show 1 or none for workers reported and the job you are looking to have done (like roofing) requires a work crew then they are sub-contracting out the work and they have no control over the quality of the job. Stay away from them.
Finally, check out the workers compensation claims. If the contractor is rife with claims they likely are not maintaining a safe work environment or are not treating their employees well.