Every processor shall keep accurate books and records which show the name and address of any producer that is selling and making delivery of any farm product to him, including the dates of deliveries, the quantities of the farm product which is delivered, and the agreed price to be paid for such farm product. If no agreed price has been arrived at, or a method for determining it agreed upon, such agreed price shall be considered the value of such product as of date of delivery. For the purpose of ascertaining such value and in addition to other evidence, reference may be had to price quotations from the federal-state market news service.