Personally, I almost never negotiate with providers in this country, but I don't subscribe to the mindset that "negotiating is disrespectful" I just find that considering I rarely book anything other than one hour appointments with providers, negotiating is unlikely to save me more than $50-100 at the most and it's simply not worth the effort to me, AND of course you run the risk of souring your experience with the girl before it even starts.
That said, if you are booking high dollar, multi hour sessions, I honestly don't see any harm in floating out a "trial balloon" to see if there is any wiggle room in the rate if you think it's more than you want to afford. I do this all the time with Sugar Babies where EVERYTHING is negotiated, but like I said I almost never book anything other than single hour appointments with providers.
The thing about negotiating if you choose to do so is to choose your words carefully, a lot of guys are very ham handed where it comes to negotiating and they come off as cheap hagglers,. what ever you do, do NOT start off the conversation by telling her she is not "worth" her stated rate, that's a way to end up on a lot of DNS lists very quickly. I'll put it to you this way, if I have to tell you the proper way to negotiate, you probably aren't tactful enough at it to be doing it anyhow. Some people can negotiate anything and not be seen as rude or cheap, other people can't negotiate the price of a used car without coming across as rude or boorish.
I don't know if I actually answered your question/s, but those are my thoughts on the subject.