Wash. Rev. Code § 11.11.040
In transferring nonprobate assets, a personal representative, a financial institution, or other third party may rely conclusively and entirely upon the form of the nonprobate asset and the terms of the nonprobate asset arrangement in effect on the date of death of the owner, and a personal representative or third party may rely on information provided by a financial institution or other party who has possession or control of a nonprobate asset concerning the form of the nonprobate asset and the terms of the nonprobate asset arrangement in effect on the date of death of the owner, unless the personal representative, financial institution, or other third party has actual knowledge of the existence of a claim by a testamentary beneficiary. A financial institution or other third party is not required to inquire as to either the source or ownership of any nonprobate asset in its possession or under its control, or as to the proposed application of an asset so transferred. A transfer of a nonprobate asset in accordance with this section constitutes a complete release and discharge of the financial institution or other third party from all claims relating to the nonprobate asset, regardless of whether or not the transfer is consistent with the actual ownership of the nonprobate asset.
RCW 11.11.040