Today a growing number of companies such as Yelp, CitySearch, Angie's List and Yahoo Local offer people a chance to rate everything from hairdressers and plumbers to child care centers and dentists.

Restaurants have been the canary in the coal mine, feeling the impact of online reviews long before other kinds of local businesses.

Because people dine out more often than they choose dentists, restaurants so far make up the bulk of online reviews. But as review sites become more established, they will gradually accumulate entries about all kinds of businesses.

For consumers, online review sites offer a valuable storehouse of information to help with daily tasks such as choosing an electrician or a dinner venue.

For small businesses, these sites have the potential to revolutionize marketing and promotion - creating unprecedented opportunities but also some unfamiliar risks.

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."

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