California Code, Vehicle Code - VEH § 9404

(a) Station wagons, except those used in the transportation of passengers for hire, are exempted from the payment of weight fees provided for in Section 9400.

Any provision of this code notwithstanding, any person (1) who is bona fide engaged in a business and who owns and operates a station wagon which is registered in the name of such business, or (2) who is bona fide engaged in a business as an employee and who is required by such employment to own and operate a station wagon, which is registered to such person, may pay the appropriate weight fees, and the department shall issue license plates of the same type as are issued to vehicles which are required to pay weight fees.

(b) For purposes of this section, “engaged in a business” means engaged in a bona fide trade, business,,  1 commerce, or in a profession in which the measurement of land, construction quantities, or the dimension of structures, is a function authorized to be performed by the license issued for such profession, but does not include being engaged in any other type of profession.