There is no exemption that is specifically issued for high sea sales. All import of goods are liable to IGST not under section 5(1) but under the proviso which takes imported goods into the Customs Act for determination of the liability. And ‘the point’ at which customs duties are levied is when bill of entry for home consumption is filed. In case of high sea sales, such a bill of entry is filed only by the final recipient (high sea buyer).
(ICAI FAQ PUBLICATIONS 06-09-2017 EXEMPTIONS: FAQ NO. 15)