There is a sort of "members guild."
Most major blogs have a list of recommended blogs that they find instructive. If you look at a number of these, you will see some names showing up frequently. These tend to be the better ones. A fraud on a widely-read blog would be nailed pretty quick. There are tens of thousands of people out there who, like those of us on this board, gain great pleasure over pointing out errors in someone else's output.
If you saw a book author recommended by many other authors, or by many librarians, it would tend to indicate that there might be something there.
Again, this is not a perfect system. But it works.