When buying the assets of a business, some are subject to sales or use tax, while others are not. Items subject to retail sales tax.It is measured on the value of products, gross proceeds of sale, or gross income of the business. Our free online guide for business owners covers Washington sales tax registration, collecting, filing, due dates, nexus obligations, and more. By mail - Download a 2024 Seattle business license tax certificate application. Then fill it out and mail it to us along with your payment. All employees of a food business must get a Washington State Food Worker Card. The Washington capital gains tax adopts the federal definition of "capital asset" when determining the taxable gain from a sale or transfer of the asset.