The commissioner or his duly authorized agent shall have full authority to investigate upon the verified complaint of any interested person, or on his own motion, the conduct and activities of any person applying for or holding a license as dealer, processor, broker, agent or retailer and for such purpose may examine the books and papers of any such person and may take testimony and affidavits thereon under oath. Any interested person who has filed a verified complaint may be a party of record to all proceedings had with regard thereto.   [PL 1975, c. 555, §3 (AMD).]