A person may not sample, haul, or test milk or milk products for the purpose of determining the value or grade without obtaining a license from the department. In case of illness or necessary absence, a licensee may appoint a substitute for a period not to exceed six days in one calendar year, unless specific approval for a longer period is obtained from the commissioner. The licensee is responsible for the acts of the substitute. An applicant shall file an application with the department stating the type of sampling, hauling, or testing for which the applicant wishes to be licensed. Before a license is issued, the applicant shall receive training in the sampling of milk or milk products as may be required by the department, and shall pass a    written examination prepared and administered by the department. The applicant must show knowledge of the requirements of this chapter and must prove by actual demonstration that the applicant is competent and qualified to perform each type of sampling and testing listed on the application. The commissioner shall issue a license which states the types of sampling, hauling, or testing for which the applicant is qualified. Additions may be added to the application form and license, without charge, after the license has been issued, upon the request of the licensee, after receiving additional training and passing the required examinations. Examinations must be given by the department at times and places as the department shall determine. A licensee is not required to take additional examinations when renewing a license unless required by the commissioner. All testers and samplers shall attend a training session sponsored by the department every two years. Retraining or retesting or both may be required when the commissioner reasonably determines it to be necessary. Licenses issued under this section expire on December thirtieth of each year. Testers’ licenses must be posted conspicuously in the licensee’s place of operation, and are not transferable. Samplers’ licenses must be carried by the sampler at all times during sampling activities and are not transferable. The annual license fee is ten dollars. A five dollar penalty fee is applied if renewals are not paid by January thirty-first.