it's mutual respect and self interest ...
IMHO ... never ASK questions before you've been screened and approved. I don't like to say never, but ... NEVER. Even after said approval, tread softly.
You might, after sharing a few ice breaker, nice to know you emails/texts/PMs, ask if you can discuss a few questions you may have about services offered that you're interested in that are reflected in her reviews. That also reflects your interest and your consideration for her boundaries.
I rarely ask, but some providers will ask to speak with you before they schedule. If they do, that would be the good time to ask questions, but again, after letting her know in advance that you'd like clarify a few uncertainties that you may have.
Just remember, no means NO! Then, the balls in your court. Now that you've gotten that far, your interest and her acceptance, I think you should follow thru and make a date. A good provider, in many instances, will appreciate your "interest" and ensure you have a great time.
After you gain a better "feel" interpreting reviews and a providers communications, or lack thereof, you'll develop a sixth sense (or a dickth sense) for knowing who you REALLY want to meet.