Hi.....
I always get the $$$$ figured out before we go to the room ,
she knows what she gets and its not a drama as she is leaving,
Many ask for "taxi money" extra , 100-200 baht, thats up to you depending on how she did and if you plan on seeing her again,
But giving a big "tip" really gets you nothing , as you are already finished with her , unless you plan on taking her some more times, but then she will expect the fee + tip every time.
I started giving one girl 500 baht more than the others , since thats what my friend gave her, and I have been stuck at that price since
not complaining too much since she is young and cute , but her friends get the standard fee .
BK