What I found from checking out tons of different gyms is it is not always about the establishment itself that correlates to the quality of instruction you'll get. I mean I train Muay Thai at a Gracie Barra gym. GB certainly isn't known for muay thai, but I knew from the first free trial class that I took that the coach was legit. The guy is no former champion or anything (mostly due to a major injury he got), but he knows what he's talking about. The average size class is like 8-10 students, never exceeding 15, which to me is important, because one of the previous gyms I checked out that strictly taught Muay Thai had upwards of 30+ students in each class. Not that they aren't receiving good instruction, I just prefer smaller classes, and the ability to have more 1 on 1 time.
Id just recommend checking out various different programs, do the free trials, then go from there.