The following persons shall not be required, but shall be permitted, to obtain licenses as licensed public weighers: (1) A weights and measures officer when acting within the scope of his official duties, (2) a person weighing property, produce, commodities or articles that he or his employer, if any, is either buying or selling, and (3) a person weighing property, produce, commodities or articles in conformity with the requirements of federal statutes or the statutes of this state relative to warehousemen or processors.