TripAdvisor is to travel as Google is to search, as Amazon is to books, as Uber is to cabs – so dominant that it is almost a monopoly. Bad reviews can be devastating for business, so proprietors tend to think of them in rather violent terms. “It is the marketing/PR equivalent of a drive-by shooting,” Edward Terry, the owner of a Lebanese restaurant in Weybridge, UK, wrote in 2015. Marketers call a cascade of online one-star ratings a “review bomb”. Likewise, positive reviews can transform an establishment’s fortunes. Researchers studying Yelp, one of TripAdvisor’s main competitors, found that a one-star increase meant a 5-9% increase in revenue. Before TripAdvisor, the customer was only nominally king. After, he became a veritable tyrant, with the power to make or break lives. In response, the hospitality industry has lawyered up, and it is not uncommon for businesses to threaten to sue customers who post negative reviews. As the so-called “reputation economy” has grown, so too has a shadow industry of fake reviews, which can be bought, sold and traded online. For TripAdvisor, this trend amounts to an existential threat. Its business depends on having real consumers post real reviews. Without that, says Dina Mayzlin, a professor of marketing at the University of Southern California, “the whole thing falls apart”.