It definitely varies from girl to girl, some may ask for extra tip to daty, some will just not have it on their menu.
Also don't assume that because you have the $ that you can get a desired session length, sometimes these girls are already booked with another client so they may only be able to fit you in for 30.
Other times they may not be available at all unless you pre-booked.
Bottom line is just be flexible and if you really want something you should check with Sara and she'll do her best to accommodate.
Also, there's many threads on this spa, I recommend checking some of those out for more current reviews.