Permissive inspection consists of inspection, including sampling and weighing, and certificating tobacco upon the request of an interested party. Upon such request, the Director may authorize and require an inspector, as a part of his duties, to supervise the preparation of tobacco to be inspected under the Act, including the sorting, handling, conditioning, or packing of such tobacco. Special tests and services may be performed for interested persons to the extent that available facilities will permit, subject to the payment of fees as provided in § 29.123.