So there are a lot of providers that don't list their rates on places CityVibe and Backpage. Some of them link to TER for reviews (so they seem legit) but still no rate. It's my understanding that asking about rates is a complete no-no and will end the date immediately. But if that's the case then how do you find out the rate? Should I bring it up or should the provider?

there should be at least one rate on her profile, can't speak for other review sites.  If she has a personal website, hopefully the rates will be posted there, although I have seen many personal websites with no posted rates.

If there are no rates posted anywhere, you have no choice but to ask.  Say something like, "What is the correct compensation for an hour of your time?"
If she hangs up, or doesn't reply to an email with an answer, it's time to move on.  After all, we ain't mindreaders......

Swim

Get the VIP, if you don't already have it.  VIP will save you a lot of grief and disappointment, and probably some serious money.  Like HH, I would hesitate to contact a provider if I didn't know her rates ahead of time.  If they turn out to be out of my budget, I have wasted my time and hers.

Two things are critical when I look at ads, reviews and rates.  No reviews, I move on.  Rates too high, I move on.  If those are ok, I look at her menu to see if my deal-breakers are included.  If they are, then I follow up with more research.

Swim

So spend the $ for VIP, plus you can read the juicy details of the reviews, which is mandatory for a great time.  Most if not all top ter providers will have their donation amounts posted somewhere, ad, website or on the profile. However, the profile donation can be incorrect.  I will not contact an escort if her donations are not posted.

If you have checked for a website or other postings and can't find a rate. Vip on TER will give you a ballpark idea and then you have to politely ask. Asking about amount to see her if she has nothing posted is OK, just don't get specific it is only the amount to see her.
Personally I liken it to one restaurant in Vegas I once went to with no prices on the menu. Basically if you had to ask you probably couldn't afford to eat there. I also don't like regular product ads where you can go page after page of information and not see a price. All of my good experiences have been with ladies who have no problem letting you know what her rates are and has them posted somewhere, even ladies who are higher then average. No posted rates anywhere have always been more iffy.

So simply asking directly like Swimtrekr describes shouldn't be a complete no-no.

Unless her rates are already posted online, in which case she might think either you haven't done your homework or you're trying to haggle or something else not worth the bother. *click*

There is nothing illegal about asking a woman how much she charges for an hour of her time.  Asking about specific questions about sexual activities is what will get you hung-up on.

Thank you all very much for your help. It was all great advice.

I don't want to talk about it, so I post it clearly in my ads.

So if rates are posted, why talk about it when it's very clear other than if you are trying to document solicitation?

That's when it's no-no.

Not posting rates is inviting the question.

that BP, Cityvibe et cetera don't allow you to post rates in your ad?  

I know BP no longer allows nudity or html of any kind.  Not even an email address much less your website on BP.  

A lot of boards/adsites can be very limiting in what they allow us to post in our ads.

Speaking for myself, when I post an ad, my intent is to get the reader to my website for the close, so to speak....