I don't think attractiveness or money plays a large part, other than the fact that you have to pay them their going rate.
For example, I am one of the least attractive guys out there. On a good day, in a dark, ambiguos setting, I would rate a 5/10. And that's if I have exceptionally nice clothes on and have just showered in the past hour. My body is very unattractive and I often am embarassed to take my clothes off, but of course, i eventually get over that when I see the girl lying on the bed naked waiting for me to join in.
As for the money, I have tipped quite alot in the past, but whether I have given the asked for amount, or I have given $100 tip, the service has never been better or worse as a result.
But I find if you treat the woman like you would treat your mother (by that I mean, with the utmost respect and admiration), then they always respond well.