IGST on high sea sales: tax collected only at first importation, incorporating value additions across pre clearance transfers. IGST on high sea sale transactions of imported goods shall be levied and collected only at the time of importation when the import declaration is filed for the first customs clearance, with value additions from each high sea sale forming part of the value on which IGST is collected. The importer clearing the goods must furnish full chain documents (original invoices, high sea sale contracts, service/commission details) to link the initial contracted price to the declared import value, and the department may reject declared value and determine customs value under Customs Valuation rules if doubts arise.