...
11.8. Information on passenger transport services can also be obtained from traveller surveys, including by means of questions on passenger fares for international transportation, although the same limitations encountered in travel would apply, namely, the capacity of the respondent to provide the correct information, and the compiler’s knowledge of the population.
11.9. An ITRS may cover most exports and imports of transport services categories, but may not properly distinguish freight exports under FOB contracts where the transporter is a resident, or imports of freight transport under CIF contracts, as the transport value is usually included in the value of merchandise. In such cases, compilers need additional information to estimate the imports of freight transport services. In addition, when using ITRS, compilers should be aware that the country of operations may be different from the country of registration or residence of the owners, especially in marine shipping.
...