It is a violation of this chapter if the applicant, or licensee, directly or indirectly, has purchased for his, or its, own account any farm product which is received by him upon consignment without prior authority from consignor together with the price fixed by the consignor or without promptly notifying the consignor of such purchase. This does not prevent any commission merchant from taking to account of sales, in order to close the day’s business, miscellaneous lots of parcels of any farm product which remains unsold, if such commission merchant forthwith enters such transaction on his account of sales.