The Washington Department of Revenue has released guidance explaining how the state's destination-based sales tax rules work.
Washington uses destination-based sourcing for sales tax. This means that the tax rate for a sale is based on where a buyer receives merchandise. For example, when a Seattle retailer delivers merchandise to a customer in Olympia, the sale occurs in Olympia. This means that the tax rate in Olympia applies. However, when a customer picks up the same merchandise at the Seattle retail location, the sale occurs in Seattle, and the tax rate in Seattle applies to the sale.
Destination-based sales tax rules do not apply to retail services, automobile towing, and vehicle sales.