In Texas, you can read a lot about the rules, etc. on this website.
http://www.dshs.state.tx.us/massage/default.shtm
Look at the links on the right, they take you to statutes, etc. Also, you can see the enforcement actions that have been taken. Some thoughts about enforcement actions:
1.) Seems to be a fair amount of attention to the Asian places. (AMPS) (They are often unlicensed.)
2.) State often uses the license statutes and technicalities to take places down rather than trying to use prostitution statutes.
3.) Male therapist seem to have a fairly high enforcement rate.
4.) I may be wrong, did not really crunch any numbers, but Houston seems to have a high enforcement rate.
5.) Most clients who visit licensed massage therapist have learned that it takes multiple visits to establish much play time. (I actually have not found that necessary, but it does seem a general rule.) LE and the State Board don't have time to concentrate long sting operations on an individual massage therapist unless they stick out like a sore thumb for some reason. (Large number of condoms in trash, close to a school, high traffic in a low traffic area might all be a sore thumb.)
Most registered or licensed therapist put a lot of time & money into their license. (I believe requirement is 600 hours of training now.) So, they don't want to blow all of that time and money by being busted. (pun not really intended.)
Hope that helps.
FYI, the massage rules does not include the prostitution laws. I think ShysterJon has posted about those before on this board. In Texas, the laws are pretty broad, pretty much any touching for sexual reasons is prostitution is money or some form of barter is involved. I think that would put prostate massage, any mutual touch, or of course any sex acts (HJ thru FS) in the category of prostitution.