Not to put too fine a point on it but if there are blind trials showing no effect and non-blind trials showing an effect, my conclusion would be the effect is a placebo.
Unfortunately, there isn't much regulation for supplements in general. Some companies do 3rd party purity testing, though it's not always the case.
This could also be explained by placebo effects.
Or if all the available trials are n<=20, I'll probably lean towards trusting the anecdotes, at least enough to try the supplement for myself.
When it comes to cheap-to-produce supplements, very limited trial data is the norm, unfortunately. There's no money for running large trials.