Any dealer in farm produce violating the provisions of section three of this act, or interfering with an agent of the department in the enforcement of this act, shall, upon conviction in a summary proceeding, be sentenced to pay a fine of not less than fifty dollars ($50.00) nor more than three hundred dollars ($300.00) and costs of prosecution, and in default of payment of such fine and costs, shall be sentenced to undergo imprisonment in the county jail for a period not exceeding thirty (30) days, and for a second or subsequent offense within a calendar year, shall be guilty of a misdemeanor and shall, upon conviction thereof, be sentenced to pay a fine of not less than five hundred dollars ($500.00) nor more than one thousand dollars ($1,000.00) or to undergo imprisonment not exceeding one year, or both in the discretion of the court.