Lots of mainstream dating advice "experts" have only have their own experiences to go on. Instead of giving any charismatic person who claims to be a successful dater a book deal and TV time,

An illustrative anecdote is that "Mystery" admits that he is actually quite bad at attracting "7s". Sure, that's hyperbole for the purpose of showing off, but there is an element of truth behind it. If he wasn't able to take on board knowledge from people other than himself and extracting the general insights then his advice would be quite limited.

On the other hand there are people like (so called) David DeAngelo who, well, isn't exactly an outlier on the 'charismatic person' scale and is more of a simple 'educator'. He just teaches the sort of classes on human behavior that would be taught in highschool if school was actually about teaching people useful stuff. He comes complete with a table of books on a variety of subjects that are well reputed in mainstream culture that he holds up, describes and recommends. Handing out assignments wouldn't seem out of place and nor would assigning pracs on 'body language and posture'. Come to think of it he does do both of those things without using those terms.

That sort of source (only PUA advice in the broadest possible usage) has a somewhat higher epistemic standard - albeit trading off somewhat on the most specific techniques by playing it safe and keeping it basic.