Avoid the big cities. I'm guessing you haven't been to Southeast Asia. It's full of marketing scams. In Pai they have smaller gyms, more personal and you get much higher quality training.
I spent a year training at Por Pramuk but Buakaw now has a gym in Bangkok it's called Banchamek Gym . Do some more research. They'll happily take your money but it's far more important you have a good relationship with your Kruu.
If they see potential in you they will train you into the ground. You'll want to die. If they aren't paying much attention to you they either don't like you or see no potential. A newer school with less known fighters might have a different take.
I second the vote for avoiding Bangkok and going to Chaing Mai. Bangkok is more expensive and you're much more likely to get involved in a scam from one of the big gyms. You'd probably have more luck going someplace like Chaing Mai or Chaing Rai and searching for well recommend small local gyms.
I am 19 years old and im just about to finish school, i have a big intrest for Muay Thai and i really want to get more intense training, and i also really want to visit Thailand, so i had the idea of going there once i've gathered the money for it (which could take 1-3 years maybe), but i need some advice about the gyms, do you have any gyms in Bangkok that you think is worth it? I've looked up "Rompo Muay Thai Gym" and it seems really good, but it costs alot, but im quite sure that it would be well spent money.
