An applicant for a milk receiver's license or for a tester's license shall file an application upon a form prescribed by the commissioner. The commissioner may decline to grant a license if the applicant has not furnished satisfactory evidence of good moral character, or if he has not furnished satisfactory evidence that he is capable of conducting the activities for which a license is required by satisfactorily answering written and oral questions prepared by the commissioner and by demonstrating the ability to conduct such activities. The commissioner may decline to renew a license or may revoke a license, after a hearing upon due notice to the licensee, when he is satisfied by substantial evidence that the licensee: