Thai VietjetAir’s official website is th.vietjetair.com, but if you google for this airline, a different (but lookalike) website comes up on top of the list - thai.vietair.com. The latter is a ticket brooker who sells at a much higher price than the airline does. It shows a very low price initially, which is then doubled by added ‘ service fees’ etc.
On the official website the price offered is the price you pay, unless you do explicitly buy extras.
Example: I booked a domestic flight to Bangkok, which on the official website costs 1563 baht. The lookalike website price for that same flight and identical fare conditions was 38 USD, which is slightly cheaper but turns out to actually be 78 USD by the time you pay. This equals just over. 2500 baht - 70% more than on the airline’s website…..