|Duty computed on gross weight of package in certain cases.
||129. Where goods liable to duty according to weight are imported in a package, and the goods are intended for sale, or are normally sold retail, in that package, then, if the package -
(a) is not marked or labelled with the net weight thereof; or
(b) is not commonly sold as containing, or as reputed to contain, a specific quantity or weight,
and in either case, the owner of the goods is unable to satisfy the proper officer of the correct net weight thereof, the goods shall be liable to duty according to the gross weight of the package and its contents.