No person, firm or corporation shall sell or offer for sale, at retail, potatoes in any package or container which is not plainly marked or labeled with the name of the official Connecticut or United States grade which represents a standard no higher than the actual grade of the potatoes contained therein, provided the term “unclassified” or “ungraded” may be substituted at the discretion of the retailer. The Commissioner of Agriculture shall enforce the provisions of this section and is authorized to establish necessary regulations therefor. Any person, firm or corporation which violates any provision of this section shall be fined not more than fifty dollars for the first offense and not more than two hundred dollars for each subsequent offense.