In the last year the Thai immigration checks have ramped up. I was a paying guest, but still got questioned and had to provide travel and hotel evidence I was a tourist. Why, I had “instructor“ on my T-shirt.There are some Thailand ops that do this (see link in my prior post in this thread). Not sure all of the ins and outs of Thailand immigration law, but I'm assuming they might justify it as folks in some other countries do -- just say that the practical (work) is part of the class, and not a paid position.