Wash. Rev. Code § 63.14.152
The seller, holder, or buyer may bring an action for declaratory judgment to establish whether service charges contracted for or received in connection with a retail installment transaction are in excess of those allowed by chapter 234, Laws of 1967. Such an action shall be brought against the current holder or against the buyer or his or her successor in interest or, if the entire principal balance has been fully paid, by the buyer or his or her successor in interest against the holder to whom the final payment was made. No such action shall be commenced after six months following the date the final payment becomes due, whether by acceleration or otherwise, nor after six months following the date the principal balance is fully paid, whichever first occurs. If the buyer commences such an action and fails to establish that the service charge is in excess of that allowed by RCW 63.14.130, and if the court finds the action was frivolously commenced, the defendant or defendants may, in the court's discretion, recover reasonable attorneys' fees and costs from the buyer.
RCW 63.14.152