Its a subject that I've been thinking about lately due to some bad experiences with the last few providers.  I sometimes think tipping up front may ensure a better session, but also risking getting ripped off.  In my experience, there is no way of getting a refund for poor performance no matter what the circumstance is.  I always tip at the end of the session based on the hole experience, attitude, performance etc.  

Comments, suggestion are appreciated.

be welcomed by the lady you're visiting. Bringing flowers or a small box of Godiva is a great way to put a smile on her face and break the ice when meeting for the first time. It shows you're a gentleman. Little things like that makes the girls very happy and warm during your sessions. Now, if you liked the girls performance, didn't bring any gifts but wants to tip, then do it at the end of the session. If your intention of tipping at the beginning of the session is to assure a good time with her, then do not put inside the envelope. Most of the girls do not touch it until you're gone, so lay the envelope on the table and the tip over saying "I didn't have time to pick up some flowers for you, but I'm giving you extra so you can pick something nice for you". Girls always remembers the guys who are nice and treat them properly and will give them a more personal and intimate attention when they return.

tip at the end if you want it isn't necessary.
If you had a good time a tip is always nice.
Gina

I have always seen tips as gestures of appreciation for jobs well done.  I am speaking of tipping in general, not only as they pertain to this circumstance.  We as a society have created an atmosphere where tips are given regardless of quality of service, and appreciation or satisfaction is reflected through the relative size of the tip.  Therefore, I always tip, and I always tip after the services are rendered.  I have always assumed that a good tip is distinguishable by the receiver from a bad tip, and that the level of my appreciation is fairly clear.  My hope is that after a good experience, and a good tip, that future services from that provider, at that restaurant, by that auto mechanic, etc. will be given a little more attention than usual and will, therefore, be a little more special.