Swim and others are better at these Qs, but I'll take a shot. Review guidelines stipulate: "In order to keep our performance ratings consistent, we set up the following system: An escort provider may only earn up to a 7, unless she also performs the following during a session: Kisses With Tongue, Bare-Back Blow Job, Really Bi, Anal Sex, or More than One Guy. The addition of each offering will raise her score by one point. If your review doesn't already accurately reflect this rating system, we will adjust it."

Clearly, the highest Performance Rating for massage only is 7. 7 is a good score no matter what, so you can consider a 7/7 to be like a 10/10, sort of. I'm guessing that a good massage (as in good therapeutic massage) will get high marks (7/7) and a good, happy ending to the massage will also help to get high marks (7/7).  

Crappy massage will merit something lower than 7/7 and an unhappy ending might take away points. While a 5/7 or a 6/7 might feel disappointing because it seems like a 5/10 or 6/10, you have to remember the 7 point maximum.  

I think others will chime in with better explanations and criteria