When doubt or differences arise as to the correctness of the net or gross weight of any amount or part of any commodity, produce or article for which a certificate of weights and measures has been issued by a public weighmaster, the owner, agent or consignee, upon complaint to the Commissioner of Agriculture and Industries or his assistants, may have such amount or part of the amount of any commodity, produce or article reweighed by the commissioner, his assistants or a public weighmaster designated by him, the services for which reweigh, when performed by the commissioner or his assistants, shall be gratis.