Wash. Rev. Code § 27.12.305
Any public library, including the state library created pursuant to chapter 27.04 RCW, shall have the authority to provide for the sale of library materials developed by the library staff for its use but which are of value to others such as book catalogs, books published by the library, indexes, films, slides, book lists, and similar materials.
The library commission, board of library trustees, or other governing authority charged with the direct control of a public library shall determine the prices and quantities of materials to be prepared and offered for sale. Prices shall be limited to the publishing and preparation costs, exclusive of staff salaries and overhead. Any moneys received from the sales of such materials shall be placed in the appropriate library fund.
Nothing in this section shall be construed to authorize any library to charge any resident for a library service nor to authorize any library to sell materials to a branch library or library which is part of a depository library system when such materials may be distributed free of cost to such library nor shall this section be construed to prevent, curtail, or inhibit any free distribution programs or exchange programs between libraries or between libraries and other agencies.
RCW 27.12.305