The second way is to rely on their reputation. If lots of people report that they did a good job in this field, you might have some reason to judge that they are indeed expert in that field. You might pick a plumber based on online reviews of their work, for example.
However, this method is subject to fraud. Online reviews can be concocted. What happens when a large, overlapping class of fakes mutually reinforce each other's claims to expertise?
The farce that has passed for public discourse the last two years was fueled by a concerted effort of the media and the pundit class to obscure gaping holes in logic as well as law. And yet, they all appeared to be credible because the institutions sustaining them are credible.What to do about that? You can become expert yourself, or develop a better network of validators.
Michael McFaul was U.S. ambassador to Moscow—he knows everything about Russia. He wouldn’t invent stuff about national security matters out of thin air. Jane Mayer is a national treasure, one of America’s greatest living journalists who penned a long profile of Christopher Steele in the pages of the New Yorker. Susan Hennessy is a former intelligence community lawyer, who appears as an expert on TV. And how about her colleague at the Lawfare blog, Benjamin Wittes, a Brookings Institution fellow and a personal friend of James Comey? You think he didn’t have the inside dope, every time he posted a “Boom” GIF on Twitter predicting the final nail just about to be hammered in Trump’s coffin?
Many more jumped on the dog pile along with them, validating each other’s tweets and breathless insider sourcing. The point was to thicken the echo chamber, with voices from the right as well as the left in order to make it seem real. Hey, if this many experts are saying so, there must be something to it.
Except, there wasn’t—ever.

