Commercial tenanciesin WA are purely creations of contract. There are no statutes designed like the Residential Landlord Tenant Act to place limits on rental agreements to protect renters. Quoting the RLTA will get you nowhere.
Your complaint is with the tenant, it sounds like. You can certainly write them a demand letter regarding any personal property left inside the space (see Replevin under Title 7). Replevin shifts fees and costs to the defendant but *may* require you to post a bond. You can review your contract to determine what responsibilities they had towards you.
In order to formulate a lawsuit you need three things: a genuine complaint, a defendant and the defendant has to have some assets you can go after (or at minimum, insurance).
People who cannot pay their rent frequently are on the verge of bankruptcy and this debt is likely to be bankruptable.
Hope this helps. Elizabeth Powell