The department's inspectors shall, at terminal warehouses, have exclusive control of the weighing, inspecting, and grading of the commodities that are included within the provisions of this chapter: PROVIDED, That official supervision of weighing under the United States grain standards act shall be deemed in compliance with this section. The action and the certificates of the inspectors in the discharge of their duties, as to all commodities inspected or weighed by them, shall be accepted as prima facie evidence of the correctness of the above activity. Suitable books and records shall be maintained in which shall be entered a record of each inspection activity and the fees assessed and collected. These books and records shall be available for inspection by any party of interest during customary business hours. The records shall be maintained for periods set by regulation.