Integrated Goods and Services Tax on high sea sales is collectable only at the time of importation, covering value additions. IGST on high sea sales of imported goods is levied only once at the time of importation when import declarations are first filed; value additions from each high sea sale are included in the value on which IGST is collected. The importer filing customs entry must produce the chain of documents (original invoice, high-seas-sale contract, service charges/commission details) to link initial and last transaction prices, and authorities may reject declared values and determine price under the Customs Valuation Rules when doubts arise.