Communication between agencies in different countries is even more difficult; in particular, customs departments rarely, if ever, check whether what they record as imports from a given country is the same as is recorded as exports by the same country.
不同国家各机构之间的联系甚至更为困难；特别是，海关部门很少、甚至根本没有核对它们关于某一国家的进口记录是否与该国出口的记录相同。