The board may hire one or more appraisers accredited by the department of revenue or certified by the Washington state department of licensing, society of real estate appraisers, American institute of real estate appraisers, or international association of assessing officers, and not otherwise employed by the county, and other necessary personnel for the purpose of aiding the board and carrying out its functions and duties. In addition, the boards of the various counties may make reciprocal arrangements for the exchange of the appraisers with other counties. Such appraisers need not be residents of the county.