If the business did a work of improvement on your property (deck construction) and it is not to your satisfaction, you need to contact the Washington State contractor's licensing board to see if this business is a licensed contractor. If it is, it was required to have written contract with you for the work of improvement.If it is not a licensed contractor, potentially the work it did for you required a contractor's license and it has no license it cannot bring a lawsuit against you for unpaid services. This is so in California. If this is true, you might want to write the business about this issue. If you do, keep a copy of the letter for future reference.If the business threatening to sue you for faulty work is a licensed contractor in your state, call the state contractor's licensing board and make a complaint against it for faulty workmanship and its failure to rectify the problem.You might consider consulting with an attorney about the suggestions I have written about in resolving the dispute. Good luck.