Section 6. Whenever the commissioner shall have reason to believe that any such person has engaged or is engaging in this commonwealth in any unfair method of competition or any unfair or deceptive act or practice whether or not defined in sections three or four and that a proceeding by him in respect thereto would be to the interest of the public, he shall issue and serve upon such person a statement of the charges in that respect and a notice of a hearing thereon to be held at a time and place fixed in the notice, which shall not be less than twenty-one days after the date of the service thereof.

At the time and place fixed for such hearing, such person shall have an opportunity to be heard and to show cause why an order should not be made by the commissioner requiring such person to cease and desist from the acts, methods or practices so complained of. Upon good cause shown, the commissioner shall permit any person to intervene, appear and be heard by counsel or in person.

Nothing contained in this chapter shall require the observance at any such hearing of formal rules of pleading or evidence.

The commissioner, upon such hearing, may administer oaths, examine and cross-examine witnesses, receive oral and documentary evidence, and shall have the power to subpoena witnesses, compel their attendance, and require the production of books, papers, records, correspondence, or other documents which he deems relevant to the inquiry. The commissioner upon such hearings, may, and upon the request of any party shall, cause to be made a stenographic record of all the evidence and all the proceedings had at such hearing. If no stenographic record is made and if a judicial review is sought, the commissioner shall prepare a statement of the evidence and proceeding for use on review. In case of a refusal of any person to comply with any subpoena issued hereunder or to testify with respect to any matter concerning which he may be lawfully interrogated, the superior court of Suffolk county or the county where such party resides, on application of the commissioner, may issue an order requiring such person to comply with such subpoena and to testify; and any failure to obey any such order of the court may be punished by the court as a contempt thereof.

Statements of charges, notices, orders, and other processes of the commissioner under this chapter may be served by anyone duly authorized by the commissioner, either in the manner provided by law for service of process in civil actions, or by registering and mailing a copy thereof to the person affected by such statement, notice, order, or other process at his or its residence or principal office or place of business. The verified return by the person so serving such statement, notice, order, or other process, setting forth the manner of such services, shall be proof of the same, and the return postcard receipt for such statement, notice, order or other process, registered and mailed as aforesaid, shall be proof of the service of the same.