As of July 1, 2008, the Washington Department of Revenue no longer requires resale certificates to be renewed every four years. The provisions of the resale certificate apply to all sales transactions as long as the seller has a “recurring business relationship” with the buyer. A “recurring business relationship” means at least one sale transaction within a period of twelve consecutive months. (WAC 458-20-102, Washington Department of Revenue, effective November 16, 2008)