Wash. Rev. Code § 19.56.020
If unsolicited goods or services are provided to a person, the person has a right to accept the goods or services as a gift only, and is not bound to return the goods or services. Goods or services are not considered to have been solicited unless the recipient specifically requested, in an affirmative manner, the receipt of the goods or services according to the terms under which they are being offered. Goods or services are not considered to have been requested if a person fails to respond to an invitation to purchase the goods or services and the goods or services are provided notwithstanding. If the unsolicited goods or services are either addressed to or intended for the recipient, the recipient may use them or dispose of them in any manner without any obligation to the provider, and in any action for goods or services sold and delivered, or in any action for the return of the goods, it is a complete defense that the goods or services were provided voluntarily and that the defendant did not affirmatively order or request the goods or services, either orally or in writing.
RCW 19.56.020