Just as you would find in almost any profession in the service industry, gratuity is typically something that a massage studio or therapist expects from clients. Despite this, there are many aspects to the expectation of tipping that I don't agree with on a personal level which is why I've opted to go with a No Tipping policy in my practice.
One of the most important aspects to a healthy client/therapist relationship is clear, open communication but the subject of tipping and gratuity is often considered taboo. And, while gratuity should be and most often is intended as a little bonus for a job well done or great service, at many studios and practices the session compensation for therapists makes gratuity less of a bonus and more a necessity for earning a living wage.
It's also no secret that good massages are typically not cheap. Plus, massage is something that works best for most people on some sort of semi-regular routine. That extra $20-$30 dollars that is *nudge nudge* "Not expected" *wink wink* after every session can really add up over time.
Considering all of this is what ultimately led me to my decision to go with the No Tipping policy in my practice. All my rates are as advertised, as are my session times...but that I think may be a post for another day :)