(a) person liable to pay freight is individual or HUF (b) Person liable to ay freight is outside taxable territory (like J&K, Nepal, Bhutan, Bangla Desh, Pakistan etc.).
Refer articles on GTA for more . . https://www.caclubindia.com/articles/service-tax-on-gta-a-guide-19063.asp . . http://www.dateyvs.com/service-tax/important-taxable-services/transport-related-services/ . .