Washington State Department of Agriculture (WSDA)
By Washington State law, the act of inspecting for pests, their signs, or conducive conditions requires one to be licensed by the WSDA. In addition, structural pest inspectors must be bonded or insured and must use WSDA-issued Inspection Control Numbers.

Home Inspector Licensing and the Existing Structural Pest Inspector License
Frequently Asked Questions from Washington State Department of Agriculture.

WA Department of Licensing Home Inspectors information
How to get a license and how to renew a license?