Almost as bad as an NRCS stop, a Customs stop (normally before NRCS sees the goods) can be just as damaging.
Incomplete/missing/fraudulent paperwork accounts for a significant part of Customs holds. More often than not, average customers aren’t aware of the documents required for a smooth import or export. Since improperly declared goods (including spare parts, personal belongings, or anything else you would like to ship in a container) may raise eyebrows with Customs.