Initially I used to tip everyone, I still do, but not as frequently and generously. I used to tip upfront too, but then I stopped that practice because not all of them leave a smile on my face with their service. I used to do that because I am getting a bit older and forgetful and I used to forget to tip at the end of the session.
As a rule, if I go see someone at an agency (which I rarely do now), I would tip the lady, if I am happy with everything, that is.
As far as indie girls are concerned, If I am not too happy with an indie, I won't tip. If she is nice, I do tip, sometimes, something that I think is appropriate and honestly, it also depends on how warm my wallet is on that day. But if I am happy I would repeat her once, twice or some of them as many as five times. For me that is the tip in itself.
But $100???? I .... think that is a bit steep. So if you see someone at 300/hr you tip her 33%? Well, I guess... I am the cheap kind. But the lady I see can make 20 or 40 bucks more in our first meeting or rather have me come see her again a few times.
