Five years ago, an ambitious restaurant owner had to worry about the verdict of a handful of professional reviewers at magazines and newspapers. Now that owner faces the judgment of thousands of potential amateur reviewers.

"In this day and age, there's nowhere to hide," said Melinda Lucas, owner of Paneless Window Cleaning, a Seattle business that has attracted a significant number of customers through positive reviews on sites like Judy's Book and Angie's List. "Anyone can give you a review that can totally make or break your business. It's made it so you have to be A+ on the ball all the time."

Len Handeland, owner of Utopia Salon near Union Square, revamped his Web site to allow online appointment booking and started advertising on CitySearch in May. He estimates that the hair salon is getting five or six new clients every day from online review sites -- enough to hire three additional stylists.

"People see our ad on CitySearch, look at our 9.9 rating, and then at the user reviews," he said. "We have 36 reviews, and out of 36 there is not one negative comment. We have seen our revenues grow by three or four times the amount we budgeted on CitySearch advertising. It has really, really paid off. "

Sites like Shopping.com’s Epinions have other methods to bolster the credibility of reviews, like popularity ratings for individual reviewers, but others, like Shopzilla, lack such features.

Mr. Chen and other executives pointed out that retail sites tended to generate more product reviews than comparison sites and even sites like Epinions, where products like dog toys are barely represented. But that alone is not enough to entice Mr. Hurt, of Bazaarvoice, to try to compete with those sites.

A number of these including restaurants only, but others have a wider range. If you’re a business owner, how would you feel about customers posting reviews of your business in sites like these? Hopefully good, because people will post reviews whether you want them to or not.