If there is a dispute or disagreement between a consignor and a commission merchant arising at the time of delivery as to condition, quality, grade, pack, quantity or weight of any lot, shipment or consignment of farm products, the Commissioner shall furnish, upon the payment by the requesting party of the necessary expenses, a certificate establishing the condition, quality, grade, pack, quantity or weight of such lot, shipment, or consignment. The certificate shall be prima facie evidence in all courts of the Commonwealth as findings at the time such inspection was made. The burden of proof shall be upon the commission merchant to prove the correctness of his accounting as to any transaction that may be questioned.