In the beginning, Web site owners posted words and pictures on their pages. Today we refer to that primitive time as Web 1.0.

In the modern world of Web 2.0, though, the audience provides the material. Many of the biggest names on the Web fall into this category: Facebook, eBay, Craigslist, YouTube, Flickr, and so on. In each case, the Web site owner provides nothing but a forum for strangers to connect.

One of the most fascinating tributaries of the Web 2.0 river is the citizen review site. One Web site after another harnesses the collective wisdom of thousands of delighted or disappointed customers. Never again will you make a mistake by choosing the wrong vacation spot (TripAdvisor), restaurant (Yelp), movie (IMDB), car (Edmunds), contractor (Angie’s List), app (iTunes), book (Amazon), doctor (RateMDs) or malt beverage (RateBeer).

If you are that hotel operator, restaurateur, car dealership or what­ever, the rise of the citizen review site is a sobering development. No longer are you on top of the mountain, blasting your marketing message down to the masses through your megaphone. All of a sudden, the masses are conversing with one another. If your service or product isn’t any good, they’ll out you. If you are a prospective customer, on the other hand, citizen review sites seem like gifts from heaven. These days if you go to a restaurant with slow service, it’s your own darned fault. You could have avoided that outcome by consulting the masses in advance.

It makes you wonder how relevant, exactly, the solo critic is anymore. I mean, if you read a movie review in the newspaper, well, you are taking your chances. Maybe the movie critic just broke up with someone or hated the movie’s director back in film school or just doesn’t share your taste. But when you’re reading the summarized assessments of 11,000 people who have seen the same movie, it’s much harder to go wrong. The kooks on either end cancel each other out, and the big middle ground gives you a pretty accurate assessment of the movie’s real worth. (On IMDB—the Internet Movie Database—High School Musical 3 earned 3.8 out of 10 stars from the 19,600 people who have voted. This reviewer feels that’s absolutely right.)

But what about the fake-review scandals that surface with alarming regularity? Yelp, TripAdvisor, Amazon and other sites have all endured accusations that phony reviews are poisoning their posts. Big dollars are at stake. No wonder merchants, using fake names, sometimes post positive reviews for their own products or companies or trash their competitors. (Internet wags have dubbed this practice “astroturfing.” Get it? Fake grass roots?)

There are some sneaky biases at work, too. Ever notice how many apps on the iTunes Store seem to score mostly either one- or five-star reviews? How could so many apps be so polarizing?

They’re not—it’s just that online reviewers are a self-selecting bunch. You’re more likely to review something if you’re fired up about it, one way or another; the vast, quietly contented multitudes generally don’t bother.

(For a while, Apple tried to address this problem by prompting customers to rate an app at the moment they deleted it. App developers cried foul. “You’re making our reviews skew negative,” they said, “by asking this question at the moment people are deleting our apps! If they liked it, they wouldn’t be deleting it!”)

How do we maintain the power of online reviews while minimizing the abuses? For starters, we can encourage voters to use their real names, as Amazon does. Yelp and TripAdvisor say they have staffers and software dedicated to zapping bogus reviews. Yes, it’s an arms race, but review sites know that their credibility is essential to their survival.

You can improve your fraud-detection skills, too. Sometimes you can just tell when a review seems overly enthusiastic. And often you can click reviewers’ names to see what else they have written. If there aren’t any other posts, that’s a red flag.

Finally, quantity matters. If only a couple of reviews seem especially positive or negative, your spider sense should tingle. On the other hand, dozens or hundreds of reviews reduce the effects of self-interested postings.

Listen: the old-fashioned system of professional critics wasn’t foolproof, either. You never knew what conflict-of-inter­est shenanigans were at play. At least in the Web 2.0 world, the crowd’s voice generally drowns out the solo voices of the untrustworthy. You’re left with a pile of opinions that contains more truth than falsehood.