If any person related within the third degree by blood or marriage, as computed by civil law, to any member of the board, or if any person that is associated in any business or partnership with any member of said board, shall be employed in good faith by any school book company, firm, corporation or agent in connection with the adoption of textbooks within this state, the said member of the board so related by blood or marriage, or so associated in business or partnership with such person, shall not vote in the rating and adoption of any school book or books offered by such school book company, firm, corporation or agent for adoption.