(3) A person who refuses or omits, without sufficient cause, to attend at the time and place mentioned in the summons served on him or her, and a person who attends, but leaves the commission without the permission of the commissioners, or refuses without sufficient cause to answer, or to answer fully and satisfactorily to the best of his or her knowledge and belief, all questions put to him or her by or with the concurrence of the commissioners, or who refuses or omits without sufficient cause to produce any books, plans, or documents in his or her possession, or under his or her control, and mentioned or referred to in the summons served on him or her, and a person who at any sitting of the commission, wilfully insults any commissioner, or the secretary, or wilfully interrupts the proceedings of the commission, is liable to a fine of $120.