Statements of charges, notices, orders, subpoenas and other processes of the commissioner under this uniform trade practices act 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 service, 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.