It may be irrelevant to your analogy (it'd be more difficult to identify "personal bias" in reviews of people, after all), but the "20% of Yelp reviews are fake" meme is highly misleading. The study in question looked at what percentage of Yelp reviews were hidden, by Yelp, for looking "fake."[1] This provides us with little additional information on the percentage of visible Yelp reviews (which is what most people will assume you're talking about when you say "Yelp reviews") that are fake.

It's a bit like noting that 96% of Harvard applicants are rejected and concluding that "96% of Harvard students didn't deserve to get in," with the caveat that by "Harvard student" you mean "a student that applied to Harvard."

[1] http://people.hbs.edu/mluca/FakeItTillYouMakeIt.pdf