How much to tip is a question?

At an MP when the girl gives her options is that a tip or an extra? If she says $20 etc for options should one tip if service is above and beyond.

I believe that when we pay the entrance fee it is for a massage only and generally non negotiable. When we get the option list it is for a service and can be negotiable. the question is should there be a tip or not.

I have been to many "legit" massage studio's here and while travelling and after paying $100 plus for a therapeutic massage left 20-30% tip.