It used to be that simple–a landlord could screen for criminal history so long as the landlord treated all applicants the same without regard to race, religion, etc. Not anymore.
Any landlord’s policy regarding criminal history must flexible enough to take into account the severity of the conduct, how recent the conduct occurred, and the rental applicant’s history since.
Landlords should also avoid using arrest records (as opposed to convictions). An arrest prove nothing, except that someone was accused.
This is true not only in Seattle, but everywhere in the United States. In Seattle, residential landlords may not use criminal history at all, with some very narrow exceptions.
Read more about criminal history use in tenant screening here.