I get massages often. My body is so stiff that there's a lot of muscle that needs loosening.
Every time I get a massage, I need to judge whether this therapist is any good. Of course, I could rate them by how much better I feel right afterward, but that's subjective and can vary from day to day, so it's hard to use as the only criterion. I don't know much about massage. So how can I tell how skilled a massage therapist is?
One way is to look at the consistency of the massage. For example, I check whether they use the same movements on the left and right sides, and whether the number of repetitions is steady when they perform a given movement. The counts on the two sides may differ, and if the side that got more work turns out to be the knottier one, I can rate the therapist more highly.
In this way, even without any knowledge of massage, you can assess a therapist's skill through the consistency of their actions. This method works not only for massage but in other fields as well.
For example, when someone claims to be an expert, you look at the consistency between their words and their actions. Of course, expertise often operates on intuition, and to a non-expert it can sometimes look inconsistent. Even setting those exceptions aside, though, there are plenty of things you can check for consistency. For instance, whether the person's words trip themselves up.
I have seen far too many people who professed expertise but whose words and actions didn't match. They knew a great deal, yet their conduct was worse than mine back when I was a college student. I've also seen cases where the talk behind their backs was bad. That was when I started to dislike people who hold guru-like positions in the public eye.