You're discounting the possibility that "fringe" medical advice would have theoretical evidence behind it, as opposed to empirical evidence.

You're also not doing an expected utility calculation. What are the costs and benefits of following this particular bit of "fringe" medical advice? In my case, the cost was: I spent a few hours reading and massaging my arm, and discovered a knot in my bicep such that when I massaged it, my wrist pain was replicated. Benefits? I got my career back. Indeed, when I first heard about "trigger points" I thought the probability that they were legit was extremely low. But in retrospect, I'm glad I followed up all the low-probability leads that I did. In fact, I wish I'd done this sort of experimentation more and sooner--the cost-benefit analysis favored it overwhelmingly. (Unfortunately, severe depression seems to make it very hard for me to motivate myself to do things that I know have only a low probability of working.)

In fact, it could be argued that the existence of an unscientific medical practice in a society where scientific medicine is available is actually weak evidence that such practice is ineffective and possibly fraudulent.

The fact that someone is passing it off as medical advice makes the probability of it being useful medical advice way, way higher than the probability that some random string of characters is useful medical advice. I agree that "fringe" medical advice is less likely to be useful than advice you get from doctors.