If you are a native speaker, then you can do a teaching license and start working for a reasonable salary (80,000 baht and more). If you are not a native speaker, then you will always be at the same level of earning and you have minimal chances to exceed 40,000 - 45,000 baht per month. If at some point you start earning more, the school will find it more profitable to find a new teacher. You will only lose the best years of your life. Of course, dozens of teachers from the Philippines will disagree with me, but they have close proximity to their families, airline tickets are cheap, and they have minimal requirements (their country is still at a very low level of development = they lose nothing).