Each wholesaler whose name appears on the label or who handles agricultural, vegetable, herb, tree, shrub, or flower seeds subject to this subtitle shall maintain for two years a complete record of each lot of agricultural, vegetable, herb, tree, shrub, or flower seed handled. He shall keep for one year a file sample of each lot of seed after final disposition of the lot. Every record and sample pertaining to the shipment involved shall be accessible for inspection by the Secretary during customary business hours.