In an attempt to decode TripAdvisor, the Wall Street Journal interviewed heavy users and spoke to online-travel experts. The most common, and most obvious, place to start when determining reliability is to weed out reviews that are way off the mean: those that have one star when the rest are positive, or five stars when the others are mixed. That indicates either an unusual incident or a writer with some interest in the hotel, like a rival property or the general manager's friend. Other hints a review might be fake: The writer mentions a nearby property as superior, has only written about that one hotel and has only visited the site once -- on the day of the review. (You can check for other hotels a writer has evaluated by clicking on the reviewer's name.)

Next, study the reviewer as closely as the review. In February, Juan Padro, a headhunter from North Grafton, Mass., was weighing a trip to Ladera in Soufriere, St. Lucia -- a resort that elicited mixed opinions on TripAdvisor. Some guests raved about the privacy, peace and beauty, while others complained it was too much like a campground to justify the average $990-a-night rate.

Mr. Padro didn't make up his mind until he read a review entitled "What a rip off!" It said, "one of the things that MUST BE MENTIONED is the fact that the moment the sun starts going down, the beautiful chorrus [sic] of frogs starts their singing until the sun rises again. It was really hard to fall asleep with all that noise." The reviewer complained that the music and the atmosphere in the bar was "VEEEEERY RELAXED" -- and left for South Beach, Miami, two days into a 10-day stay. "The guy was so clearly a meathead," says Mr. Padro, who decided (correctly, it turned out) that any resort that would scare off someone like that would be perfect for him.

Excessive effusiveness is a red flag for Wayne Rutman, a private investor from Wilmington, Del., who is on the road every month and frequently uses TripAdvisor to plan his trips. Phrases like "dream vacation of a lifetime" and "best place I ever stayed" signal a lack of experience. People who find it necessary to say they're world travelers in the first line are also suspicious, like someone who feels the need to impress others at a cocktail party, he says.

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