I too am from WA. As far as I know, as long as they do business in this state they can be sued in this state.
Assuming it is a CA, have you checked the WA State Licencing website for CA that have been fined and/or lost their business privileges here due to none compliance?
If you are absolutey decidedly hell bent on suing, here are some thoughts;
First step to sue, dispute with CRAs. You did and good for you(if you are hell bent on suing), it came back verified.
Keep copies of the verification results from the 3 CRAs and also your credit reports before and after listing the account.
Try and apply for some card/account which would be denied because of this negative listing. Keep copies.
Goto court. 1000 bucks.
Of course its not that easy! You probably might need a lawyer or lotsa man hours of dedicated and comprehensive research.
I dont favor cunning unless i'm done wrong and my hatred for the financial system and its entities knows no bounds. We are the richest country and in the world and the second and the third don't even come close put together and still its here that theres a whole lot of people sufferring and id say because of financial abuse. I believe thats the direct or indirect cause of most of the issues we have today apropos healthcare, education, poverty etc. Not crime though cause nothing justifies crime in my books.So i'd do what it takes and perhaps sue and the objective is a negative mark(with state and public) on a company doing wrong..