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