maybe the person have been blacklisted from entering? Who knows...it's always best to apply before you board the plane better than you reach there n got denied entry.
What if your TDAC gets rejected when you apply at Thai airport? You should apply before your flight in case yours is not approved and you are still at your home country.
I just don't understand why people can afford to go holiday, yet want to save on the insurance money that really is just less than a hundred dollars??..