Everybody has an opinion about food, travel and the products they use. Online, there are plenty of places to express them.

Anyone with a smartphone, iPad or computer can write and post commentary on dozens of websites that accept unsolicited reviews of restaurants, travel, consumer products, home-repair services and many other buying categories.

Once reserved for stuffy, often anonymous critics at newspapers and magazines, such social commentary has become the avocation of millions of people. Their opinions have reshaped how businesses respond to customers, recast their marketing strategies and rewired how those looking for information find it before they buy.

For many businesses, such public scrutiny can be jarring at first. Some go on the defensive. But savvy operators use criticism as important customer feedback and an opportunity to improve.

For new businesses, reviewers add to the tension of a make-or-break situation. A positive write-up can bring new customers; a negative one can keep them away.

As the commentary culture has grown, all the opinions have influenced sales and spun off further business opportunities. They help online retailers such as Amazon.com and Overstock.com sell products to consumers, sight unseen. They also are the main attraction of review sites such as Citysearch, Yelp and TripAdvisor, which rate businesses according to the reviews and also sell them advertising and other business services.

All the openness, and all the dollars at stake, carry the potential for abuse.

Many review sites sell advertising and sponsorships to businesses that are reviewed on their sites, creating the possibility of unfair play.

Review site Yelp continues to be dogged by complaints from business owners and executives who believe they are being “blackmailed” into buying advertising.

And when anyone can post a comment, it’s possible to stack the deck with positive or negative reviews by authors with ulterior motives.

To prevent people from gaming the system, the websites employ sophisticated filters and computer programs to weed out bogus commentaries.

Influencing buyers

Anything with an address is fair game for so-called “Yelpers,” who review everything from restaurants to chiropractic clinics on the burgeoning online site Yelp .com.

Hotels, restaurants and tourist attractions are the target of reviews submitted to TripAdvisor, which is owned by travel-booking-site Expedia.

Angie’s List focuses on services providers, from doctors and dentists to roofers and house cleaners.

Other review sites include Zagat, Urban Spoon, Citysearch, Restaurant DB among countless others. Travel-booking sites, including Priceline and Yahoo Travel, also encourage travelers to post reviews.

Retailers’ market research shows that Internet shoppers increasingly rely on online reviews to make decisions and that those who browse a site’s top-rated products list were significantly more likely to make a purchase than those who didn’t. The review-readers also typically spent more per order.

Russell Dicker, director of community for Amazon.com, said that user-generated product reviews are a critical aspect of online retailers’ operations.

“They make the system work,” he said.

Product reviews helped Amazon sell more than $34 billion worth of goods via the Internet in 2010. Dicker said reviews ease online shoppers’ anxiety about buying products sight unseen and also help drive traffic to Amazon’s Web site. When people search for a product online, they often start by reading reviews which provide links to sellers.

Millions of voices

For review sites, the reviews are the main draw.

Anything with an address is fair game for so-called “Yelpers,” who critique everything from restaurants to chiropractic clinics on Yelp.com.

Hotels, restaurants and tourist attractions are the target of reviews submitted to TripAdvisor, which is owned by travel-booking-site Expedia. The estimated 45 million hotel and restaurant reviews posted on TripAdvisor draw 40 million visitors a month to its website. That traffic enabled the company to generate $480 million last year in advertising and booking revenue.

Angie’s List focuses on services providers, from doctors and dentists to roofers and house cleaners.

Other review sites include Zagat, Urban Spoon, Citysearch, Restaurant DB among countless others. Travel booking sites, including Priceline and Yahoo Travel, also encourage travelers to post reviews.

Yelp’s 17 million posted localized reviews of restaurants, retail stores and other businesses attracted 50 million visitors to its site last month, up from 46 million the month before.

Yelp is privately held and doesn’t release financials, but analysts at Up Next Research estimate the company took in $57 million in 2010 and is on target to pass $100 million by 2012.

Because of the growing importance of reviews, companies such as Amazon, Yelp and others go to great lengths to cultivate and nurture their colonies of reviewers.

Contributors can range from one-time authors eager to share a good or bad consumer experience to serial commentators such as Pennsylvania resident Harriett Klausner, who, at last count, has written 24,514 book and product reviews for Amazon.com.

While the companies typically don’t pay for reviews, top contributors at Amazon can be inducted into its exclusive Vine program and receive products from manufactures for their use and review. While Harriet Klausner is Amazon’s most prolific reviewer, A. Chandler is Amazon’s top critic, based on the 27,127 out of 27,816 readers that found her 467 reviews useful.

At Yelp, which opened a 200-plus-employee regional sales office in Scottsdale last year, so-called “elite” reviewers are regularly feted at social events hosted by the company. Yelp reviewers are nominated, sometimes by themselves, to become “elites” and are evaluated based on the quantity and quality of their reviews. Readers on most sites can rate the quality and usefulness of the critiques.

“The reviewers are constantly being reviewed themselves,” said Gabi Messinger, director of marketing for Yelp’s southwest regional office in Scottsdale.

Every day, Yelp picks a top review in each of the numerous markets it covers to be prominently featured on its site.

Sarah Grimwood has written 245 reviews of Phoenix-area restaurants and businesses since becoming a “Yelper” in 2007. Besides creating a platform for her comments, Grimwood has found Yelp an important social network and a source of many friendships.

“I didn’t know anybody when I moved here and met most of my friends through Yelp,” she said at a recent function for “elite” Yelp reviewers at Luci’s Healthy Marketplace in central Phoenix.

Andrea Karetsky, whose Yelp mantra is “party like a rock star,” has written 143 reviews and also spends a lot of time socializing with fellow “Yelpers.”

Kurdy Sin of Glendale is attracted to the writing process and constantly strives to improve his commentary.

“I love to write reviews,” he said.

Sin has created 115 reviews and hopes to have one selected as the top review of the day in the Phoenix market.

Army of reviewers

When everybody has an opinion, every business has to be on alert.

On opening night for Sam Fox’s latest restaurant, the Arrogant Butcher, there were practically as many critics as customers at the downtown Phoenix restaurant.

“They were out in force with their cellphones and iPads, taking pictures of the food and making notes,” Fox said.

His company, Scottsdale-based Fox Restaurant Concepts, operates 30 restaurants that are constantly being reviewed on Yelp and other sites.

There are 91 reviews of the Arrogant Butcher already posted on Yelp and 276 criticisms of Fox’s more established True Food Kitchen.

Fox takes his reviews in stride.

“We don’t live and die by reviews,” Fox said, offering that some can be off-base. “If we get a bad review of a restaurant that is packed every night with satisfied customers, we take it with a grain of salt.”

But he acknowledges the company can’t ignore the commentary.

“If it’s a valid complaint, we look at it as an opportunity to improve,” he said.

With more people relying on reviews to make decisions about where they spend their money, they can make or break a new business. And for entrepreneurs unaccustomed to public criticism, a bad review can be a jarring experience.

Erik Angermeier, owner of Slippery Pig Bike Shop in central Phoenix, said he was shocked when a Yelper complained about the dirty couch and being offered used parts for less money.

“Most people are happy to have the option of getting parts for less money,” he said.

Then, he said, he got a call from a salesperson at Yelp offering to “improve the company’s online reputation” for $300 per month.

“I took it as if they were offering to take down the negative review,” he said.

He turned them down and now wonders if the spate of negative reviews of his business is a result of his refusal to advertise.

Business of opinions

How opinions pop up on sites, and how the purchase of advertising can alter that, remains a big focus for the businesses being rated.

The sites insist that buying an ad or extra services has no bearing on the nature of the reviews they publish. But when a site is selling services to businesses of which it also is publishing reviews, there is at least the potential for abuse.

Basic hotel, restaurant and business listings on TripAdvisor and Yelp are free – but can be enhanced for a fee.

Businesses that advertise on Yelp pop at the top of searches, ahead of competitors with better ratings. Those businesses don’t have to worry about their listing being cluttered with Google ads from competing establishments.

On TripAdvisor, an extra fee nets a video and a link that, for example, allows customers to book directly with a hotel instead of through a booking site such as Expedia. And companies such as Expedia, which owns TripAdvisor, can pay to be listed as the top default booking site.

Restaurant-review site Zagat .com gets around the potential appearance of impropriety by charging consumers to access the site and not accepting advertising from restaurants.

Angie’s List requires reviewers to identify themselves and take an oath of honesty. Only businesses with high consumer marks are allowed to advertise.

At other sites, you have to take executives at their word that there “it doesn’t happen.”

Adam Medros, vice president of product at TripAdvisor, said that a business owner generally would not be happy with a bad review.

But he added, “There is no correlation between buying an ad and the reviews that appear on our site.”

He said the company encourages advertisers to publish a response to a negative review and to respond to legitimate criticism.

Yelp controversies

Yelp continues to be the subject of reports from small-business owners who contend that Yelp salespeople offer to hide negative reviews in exchange for advertising, a practice the company denies.

Yelp spokeswoman Stephanie Ichinose acknowledged that sales people may refer to a business’ reviews when making a sales call but never would offer to quash negative comments in exchange for advertising.

“Some businesses may leap to that conclusion, but that’s not the case,” she said.

Last year, two law firms filed a class-action lawsuit against Yelp on behalf of a Long Beach, Calif., veterinary hospital that drew that conclusion.

The suit, which accused Yelp of “implied extortion,” was dismissed by a U.S. District Court judge in April, who noted that the claims could not be backed up.

Owners of the veterinary hospital alleged that negative reviews reappeared when the business refused to buy advertising and that Yelp salespeople said they could control which reviews appeared on the site.

Yelp denied the allegations and said the business owners misunderstood how the site works.

Still, Yelp made changes. It took steps to enhance the integrity of its site by allowing access to reviews that had been flagged by its filters and quashed and also did away with the practice of allowing advertisers to feature a favorite review.

Yelp employs a complex system of algorithms and teams of investigators that weed out and remove from the site reviews that contain inaccuracies or authored by friends of the business, disgruntled employees or competitors attempting to manipulate the process.

“People can look at the reviews that get taken down and see there is no pattern of manipulation,” Ichinose said.

Gaming the system

Because anyone can post a review, it’s possible to take advantage of the system. Business owners could solicit friends to write positive reviews – or write them themselves. On the other hand, competitors or disgruntled employees could type in negative ones. Most reviews sites employ elaborate filters and algorithms to weed out potential bogus commentary.

Many of the complaints from businesses about Yelp have to do with positive reviews being taken down from the site while negative ones are allowed to remain.

“Nobody complains when a negative review gets taken down,” Ichinose said, adding that some of those positive critiques may have been written by friends of the business owner.

“It’s important to have controls in place so the site can remain trustworthy,” she said.

At most businesses, other reviewers and readers also can flag reviews that seem suspect.

At Zagat.com and other sites, flagged commentaries are turned over to a team for analysis and possible suppression.

“We’re always on the lookout for people trying to game the system,” said Tiffany Herklots, a spokeswoman for the restaurant rating site.

Ichinose acknowledged that legitimate reviews could be caught by Yelp’s filters and suppressed, but that the company continued to fine-tune and improve its monitoring systems.

“When we started in 2005, it was mainly looking at a review and asking ourselves, ‘Does this seem legitimate?’ ” Ichinose said of the review-filtration process. “Now it’s gotten very complex and a lot more accurate.”

TripAdvisor also employs computer programs and algorithms to weed out bogus reviews. On its site, hotels and restaurants suspected of trying to game the system are identified by a red badge.

“The red badge tells users that this hotel tried to manipulate the system,” said TripAdvisors’ Medros. “It’s a huge deterrent and can cost a hotel a lot of business.”

Medros suggested that instead of complaining about reviews and trying to beat the system, hotels, restaurants and other businesses should put effort into improving their products and responding to and addressing customer complaints.

“Travel is a variable experience and not every day will be good,” he said. “Most consumers realize that and look at the body of reviews and not a single out the negative ones.”

A lot of negative reviews, of course, could indicate a problem, he said.

“It is critical, then, that the owner responds,” Medros said.

Reach the reporter at max.jarman@arizonarepublic.com.