To get your money back you will have to sue in Small Claims court. Since it will be a he said she said it will come down to who has the best evidence. Bring before and after photos and any witnesses to the state of the property when you received it(any neighbors or non-related individuals will hold more weight in court. I think you have a good case; the landlord would have to show the place being quite a wreck for witholding $1300. You can sue up to 2x the cost of your security deposit in WA. Google RCW 59.18.280.