Hello Toxic,
First, let me say that a lady will never look at you as "cheap" if you don't leave a tip. I think what is most important for the ladies is to receive their full donation within the first few minutes of the encounter, without having to ask for it.
I always love to see the point of view of a provider, but i tend to disagree sometimes. Maybe its the way i learn in that business, always pay at the end to protect yourself, but i feel paying in advance, like full down payment is exposing yourself to problem, especially with somebody/agency you don't know. Its true to have the donation visible is a thing, so she can at least see the money is there, its real, but if she take the money before the meeting is started, i never like it. Money has to be discretly taken at the end, when she is dressing back, putting her stuff in her wallet. I don't mind she take it in front of me and say thanks or whatever, but at the end.
Here is how i used to do things personally. If i saw a girl with an extra avalaible, i would usually put that extra in the donation right away. But one time it was not provided, and i ended up giving away 40$ for a mediocre session... Try to remove the money from the donation... kinda look weird... On the other hand, adding the extra/tip later is not weird. Thats what i do now. I will put the base price on the night table... usually under the phone or something(sorry but i don't use envelopes...i find it silly and i rather make sure she SEE the money) and when she get to the bathroom to shower i will add the extra or the tip.
Now thats just my way, i guess its different from everybody. But i really prefer that payment be taken at the end. When i started in 2009 lots of people said "asking for payment in advance is the first sign of a bad encounter to come"
Now for the ratio of tips vs no tips, im surprise not more people tips, but then again as a booker i was told often by girls the regulars where not tippers. I won't mention a name but the worst i saw was that dude who was a guy that called often, he was not downtown, and he never had the freaking right payment on him. He asked me make sure to tell the girl that she bring change ... worst part is the ammount was 180 and he had 2 hundred bills... How hard was it to tip that 20? I mean if you have the right ammount i can understand to keeping that 20, but asking for 20$ back from an escort... when you already see her at a discounted price... now thats low. If he see that im sure he will know its himself im talking about. Im not a booker anymore, will never be again, so im not shy of mentioning it. I tough it was so cheap... Thats like asking the waitress for 1$ back if you have only a 2$ to tip... cmon.