All employees required for the proper operation, management, and control of the parking places acquired and constructed under this part shall be city employees selected as other city employees are selected. The number of such employees and their salaries shall be determined by the legislative body unless, by ordinance, which may be adopted or repealed at any time, the power to make such determination is granted to the board. Any salary or wage so fixed shall in each instance be at least equal to the prevailing salary or wage for the same quality of services rendered to private persons, firms or corporations in the city under similar employment, in case such prevailing salary or wage can be ascertained.