My site, like many others state rates are all inclusive.
On the other hand, there are services/agencies which take half the girls donations at the end of the night and she also has to pay for the room.  Tipping these ladies would be more appreciated I'm sure (personally I feel bad for them).

If you had a great time and want to tip an independent, then that is wonderful but personally I have not disliked someone because they don't tip.  To be honest, I would prefer to see a clean, fun, respectful guy over a stinky one with less consideration who does tip.  

Another option to show appreciation is to pick up a small gift be it a lottery ticket, a candle, or something the two of you can share together (toy, lotion, etc.)  If you want to show gratitude, this may be a more feasible option for some (some guys have to save a long time so they can play!)

We are all at different financial levels and if you cannot afford to there is nothing wrong with not tipping.  Many of my regulars do not tip in cash, but their friendship and loyalty mean more than any gift or amount of money.

Hope this helps.  Hugs, Kate xo