Expat salary is under the lanses of Department. The supreme court already decided in a the case of Northern Operating Systems Private Limited (NOS). In this case the amount was deemed to be service and was made taxable.
After this judgment GST dept started ending a lot of notice for GST on expat salaries. But CBIC release an instruction to not to send notices before applying the technical acumen. (public_profile can be reached at shaifaly.ca@gmail.com)
Not every case will be similar to the NOS. The decision in that particular case were given based on the facts. It may change in every other case. But in case of Mercedez-Benz, Stayed the order demanding the tax.