The Internet has fundamentally changed the way that buyers and sellers meet and interact in the marketplace. Online retailers make it cheap and easy to browse, comparison shop, and make purchases with the click of a mouse. The Web can also, in theory, make for better-informed purchases—both online and off—thanks to sites that offer crowdsourced reviews of everything from dog walkers to dentists.

In a Web-enabled world, it should be harder for careless or unscrupulous businesses to exploit consumers. Yet recent studies suggest that online reviewing is hardly a perfect consumer defense system. Researchers at Yale, Dartmouth, and USC have found evidence that hotel owners post fake reviews to boost their ratings on the site—and might even be posting negative reviews of nearby competitors.