By few I mean about 10 yrs ago or so.  

 
A frequent poster on the GD board got caught advertising at two different price points. She got her ass handed to her by very angry mongers.  She got all defensive and shit.. It was epic.  

 
If I were you, I'd book w/ the lower one and tell her where you found her ad. Take screenshot of her ad and keep it as a supporting document to justify why you are paying less.

I move along to the next provider.  

It makes me question how professional they really are if they can’t get the same info to agree between all of their ads and personal website. And this goes double for providers who have assistants.  

Besides, most providers say not to discuss money or else they will cease communication.

no no no no no no no no no no no no no no no no no.....ummm...i PROBABLY..... would choose not to visit on this tour!  

Sometimes I wonder if this is because one ad is older and they haven't updated it yet. But that's still very unprofeassional.

First, make sure both ads are recent. If so,
- contact her and reference the 600/700 ad in your message. I can't recall the last time a pro did not restate her expected rate somewhere in a confirmation message.
- if 600/700 is your limit and she comes back with  800/1,000 make an excuse to cancel.
- if I REALLY wanted to see her at 600 and she came back with 800, I might mention the discrepancy.  I had a similar situation once and the girl admitted that she changes her rates a lot based on her mood (probably based on short-term supply/demand) and agreed to the lower ad rate - and at the time, was one of the best experiences I ever had.

I would not show up expecting to pay 6 and have an awkward moment/confrontation when she asks for 8.

An ignorant monger asks a question to everyone but the person that can actually answer the question.  
Hey genius, text or email her with something like:
"Hey there___________ (fill in her name) can you please clarify your rates while you are here in__________ (fill in the city).

Any other issues I can help with?

I agree with the general guidance to move on.  But I have seen this happen many times for ladies who book through an agency. Not sure if the agency made a mistake or they were trying to game the system - especially when asking for a deposit.

 
I always google-search a providers' phone(s) and email. If I see multiple listing for different providers under the same number it's an agency.  And I try to never book through an agency if I can avoid it.  

 
I'm not comfortable asking before we meet face to face about a price - unless she communicates it first.  But I have sent a link to the ad I am using in my booking/screening message. "Hi! Saw your ad here www.herlisting.com and would like to request a meeting..."   That gives her a chance to tell me if something in the ad is incorrect before we meet. I really don't ever want to get into a conversation about the envelope being "short" because I relied on the wrong ad.  

 
Life is good

 
The Cat

Simple just ask her...

She might have different rates for different cities or she might have not updated one website.
That way there is no awkwardness during your appt time.
Just my .02