My criteria is pretty basic, I suppose.
I first read a couple of her TER reviews. After that, I go to her profile &/or website(s). I do this to see her photos and read more about her.
After doing all of that, if I'm interested in meeting her, I follow the directions that she has posted - which usually means sending her an e-mail.
When she responds, I continue to dialogue with her to get a better feel and understanding of her.
If we hit it off, then I make arrangements to schedule a meeting/session with her.
I've met a few providers thru TER, most of whom I haven't hooked up with more than once. (This is for many different reasons, none of which I'll disclose here because it would be ungentlemanly to do so.)
However, this is how I met my ATF - Miss Eva Bliss!
Like I said, pretty basic.