It is virtually impossible to open a bank account on any kind of tourist visa including visa exemption. I have heard of very few people managing to do it through an agent but. As you say. That could lead to problems later. Your best option is to leave Thailand and apply for a 90 day non o based on being over 50 from the Thai embassy where you go. I believe it can be done on line. Come back to Thailand and with that visa it should be easier to open a bank account but you might have to try a few. Put the funds required into the account for at least two months before applying fir one year extension of stay. If you don't want
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0 tied up in a Thai bank for ever or at least half of it fir 6 months then start to transfer at least
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baht a month for 12 months to get your second extension. You need to be able to prove the trandfers came from overseas. You can do what you like with the monthly transfers but leave the
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0 baht in your account for 3 months and do not allow the balance to drop below
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0 baht until you have your second extension based on monthly payments. Good luck.