Another reason to be skeptical of rave Amazon and Yelp reviews. As customer reviews have become important marketing tools, an industry of mercenary reviewers has sprung up. Entrepreneurs offer rave reviews for products and services for $5 to $10, flooding sites with five-star feedback that bumps those products to the top of the list. But Cornell researchers are working on an algorithm to distinguish between authentic and phony reviews. They found that fake reviews tended to be a narrative, heavy on “me” and “I” but light on description. Their program caught fake reviews 90 percent of the time, and immediately attracted the interest of Amazon, Hilton, TripAdvisor, and other sites.