> 2. they are known quantities. We have a certain image of Roger Ebert (as an example) in our minds and can adjust his reviews to get closer to our hypothetical opinion about the film. Also, we get to know his mannerisms and idiosyncracies.

I'm guessing choosing him as the example means he's one of the biggest names in professional critics, but he's as unknown to me as Mike from 4chan. I really do wonder how much the average person actually payed attention to critics like him compared to trailers/commercials and friends.