Spending: How Yelp works

An outsize number of Yelp reviews are the work of a small but vibrant community of consumers. This so-called elite squad writes about half of the site's restaurant reviews, according to a study by Michael Luca, an assistant professor at Harvard Business School.

Being an elite Yelper is like joining an exclusive, invitation-only club. Elites can attend what Yelp calls its "epic parties," which the firm sponsors with local businesses such as breweries and restaurants. In some cases, elites have received tickets to Broadway-style shows, courtesy of Yelp. "We don't get financial compensation, but it's a great perk," says Eric Rosenberg, 31, an elite Yelper from...