I have just discussed this with my accountant here in Australia. She has had to do similar paperwork for the same reason for a client of hers with a bank account in Greece, it is legitimate and I have been told that i must fill in the paperwork as it is an international banking agreement. Firstly if you are NOT an American or have a green card or somehow have an affiliation with tax in any form with America disregard the forms w-9 and w-8BEN, you will see on the original e-mail it states "if applicable". Write across these two requests forms as ALL NOT APPLICABLE when you send your paperwork through as they are just for the American affiliations, just fill out the individual Self-certification. As I obviously cant go to a Thai bank being here in Australia I will have a copy of my passport certified by my Tax agent and e-mail (not Happy with that). i wont be able to send mine till 3rd December so I cant tell you till after then if there has been any setbacks.
After following Aseannow members comments (and its predecessor) for the last 15+ years this is my first post.☺️