Good question.  I do about 80-90% of my hobbying strictly off of the pages of TER. But I keep my eye on BP and CV.  I'm done with EROS.  I've yet to find a real hidden gem on those pages but I have had some fun there.  There's something to be said for the excitement of a totally unreviewed provider.  No telling what's behind the door.  Is it an LE trap?  Some thug with a gun looking to rob you?  Julia Roberts from Pretty Woman?  No telling.  Needless to say what I've usually found are semi-pros.  Most have been in the biz a little little while but haven't gone fully pro yet.  Or maybe a better analogy is they're AAA ball players.  Maybe they have too many rules to really catch on as solid indy providers, or they're not educated/savvy enough to build their own web pages, get decent pics and market themselves through sites like TER.   Most of the time the worst that will happen is you'll be a little disappointed and you'll say to yourself "damn, why didn't I spend the extra $ and go with a TER reviewed provider.  Occasionally you'll get ripped off and there's always the possibility you'll get arrested or shot.   My advice:  Stick with TER reviewed providers and you won't go wrong.  If you're interested in the thrill of the unknown then venture into the wilds of BP and CityVibe.

It's not impossible to find a new-ish provider on BP or something similar, but the odds are against you.  Do your homework -- google the number, check the pics, evaluate the writing style.  You'll find that the vast majority of the ads you see are either fakes, or providers with some history.  

That's not to say that you won't run across the occasional part-timer or newbie.  I have very fond memories of an afternoon spent in a dorm at Goucher College having a great time with a cute coed.  Still, that's very much out of the ordinary.  There's a big difference in "these pics are very amateur because I'm new" and "these pics are very amateur because I can't manage to get my act together enough to take pictures with anything besides my phone".