Supplement Laws

As a university student,  in some of my nutrition classes we've studied the supplement act of 1994. Several of my professors basically explain it as supplement companies being able to sell dirt in a bottle and call it a supplement. As a bodybuilder and someone whose taken supplements like BCAAS, preworkout etc for years, I'm curious how true their explanation is? I'm picky about what I take, hence why I use MTS, but from your experience what regulations/requirements do supplements have to meet/pass before you can sell them to the public? And what standards do supplement companies like MTS hold themselves to that maybe aren't necessarily required by law?