Feedback helps, but makes no difference with those who have been members a while and have no FB themselves. From chatting with girls over the years, they do get a lot of emails and sometimes have to filter them. You might think its bad business but if they're getting enough clients then its clearly no problem from their perspective.
I usually go for the phone, but use emails a lot to sound girls out and get a decent reply rate but my FB is over 30. Just don't be a knob, and the key thing is, if you're asking questions, also mention you want to book, a duration and a specific day. Put this in the title too. This doesn't bind you mind!