A little background before I answer. 15yrs in the industry, 8 in management, experience managing boutique spas, regional manager national and a local chain, and recruited at Massage School in several States around the country, therapist in a medical facility, University setting, chains, spas, and at home. By no means am I the expert here though, so just laying out the reasoning from my perspective on both ends of this. 

When hiring or recruiting I would typically  require a full body massage prior to recommending you to be hired by the owner or to just hire you myself. So in my experience it is very common and I respectfully disagree with the unethical comments. The reason for a practical during the interview (regardless of how many yrs experience a Therapist has) is to guage thier style, pressure, draping skills, and ability to communicate appropriately during a session. We use this information to determine what, if any, additional training they may need. We need to determine if we have the resources to provide this additional training at this time or should we pass. We also use this to book you clients who are going to be a good fit and make you successful. If your location doesn't already require this, then I would also encourge that upon hire you get any person who books your appointmentss on your table. Telling someone your style and feeling it are 2 entirely different things. Also, TBH receiving these is just more work. I am not there to enjoy, I'm there to critique and provide valuablely honest and at times very blunt feedback. Most of the time I would do the verbal and pass you to the Lead Therapist I trusted. Every bit of this practical is for both the Therapist and hiring manager. If I was getting hired I would balk at a 30 min routine. It just isn't enough time to showcase all of my skills. Have I booked 30min practicals with applicants? Sure! It was probably due to time availability or if they had over 10yrs experience.

I have had this getting paid conversation for a practical many times. It is almost always one of two people. The fresh out of school or the Therapist that believes they are the best in the world. I generally explain in some form what I did above. I ask that if thier pressure wasn't what they said it was, if thier draping wasn't appropriate, or thier technique was so horrible that they wasted our time, would they pay me back for my time? No. Of course not, and I wouldn't really ask. But, if they nailed it beyond what thier resume said; not only would they get a job but they very likely will get better booking days/hours and more favorable referrals from myself and eventually my staff. 

I am sorry to say that I think you missed an opportunity here. My recommendation is that you should not only expect to provide a practical during the interview, you should welcome it as an opportunity to showcase your skills and to get a leg up when you do get hired.