Upon the trial of an action for any of the sums forfeited, as provided in Sections 7814 or 7815, proof that the person demanding or receiving the money as fare, or for the sale of the ticket or check, was at the time of making the demand or receiving the money, engaged in an office of the corporation, or vehicle belonging to the corporation, shall be prima facie evidence that such person was the agent, servant, or employee of the corporation, to receive the money, and give the ticket or check mentioned.