Unlike some, I do consider it impolite and inappropriate (and unsafe) to start talking money with a provider I have never met, so if I find different numbers in TER, P411 and her web site, my approach is as follows.
The number in her TER Profile is maybe a guideline, but nothing more. The woman can't change that rate at will. She can ask to have it changed, but that'll happen if and when it happens. Some women don't even look at TER so the number could be as old as her first review. If the low number is in her TER Profile I ignore it.
As between P411, a recent ad in TER, and a personal website, I consider the lowest rate to be fair game. When contacting her, I mention the place where I saw the lowest rate. I don't mention the number, obviously, but I expect her to know what is in her postings and if she doesn't like that rate it is up to her to say so. The same would be true of Eros, or Date-check or other ad sites.
One time I sent a P411 request which was accepted. The next day I noticed she had increased the P411 rate to the rate on her web site, but she didn't say anything to me about it. I brought the rate in place when I sent my request. I mentioned it at the end of our date so she would not think I was intentionally shorting her, or had brought the wrong amount by mistake. She didn't complain or seem surprised. If she had I would not have been sympathetic. The next time I saw her I brought the new rate.
Caveats. If an ad has a date on it and is more than a couple weeks old, I don't rely on it. If a rate is stated to be a special offer for a limited time, I won't even mention it once the time has passed. And, I don't rely on typos. If she dropped a zero by mistake, or if the discrepancy is just unrealistically large, I point it out to her.