Private car sales

Washington State[ I bought a car grom a private party and when I went to transfer the vechile into my name I was told there was a lien on the title. I contacted the lien holder and they said they would release the title to me for $500, which I am unable to do at this time, I then notified the seller of the problem they of course acted as if they were unaware that any lien exsisted. Which I now know they were aware of when the vechile was sold to me. Isn't it illegal to sell a vechile without disclosing a lien exsists? And isn't it the sellers responsability get the title cleared? I would think it is a type of fraud because I was never made aware that lien exsisted.