The sector became a hot area of the internet economy. Yahoo bought Kelkoo in 2004 for about $550 million, before it was sold again in 2008 to the British private equity firm Jamplant for less than a quarter of the price amid wider problems at Yahoo. Also in 2008, Microsoft bought the owner of Ciao.com, a European competitor, for about $490 million.
But in February 2011, the traffic that Google sent to Kelkoo and others tumbled. Google had a similar shopping service and was now putting its own listings at the top of search queries.
“It basically smashed the market,” said Mr. Stables, the company’s chief executive. “Our free traffic that came from Google dropped by 92 percent in two or three years. Our revenues took a massive hit.”
He closed offices in Germany, Denmark, the Netherlands, Sweden and Spain. More than 150 people were laid off. Mr. Stables and others took their complaints to regulators in Washington and Brussels, arguing that Google was abusing its dominance by changing its search algorithm to force its way into new markets like shopping, travel and restaurant reviews.
“We were just the tip of the iceberg,” Ms. Raff said. “We are one of hundreds or thousands of companies that have been hurt.”
To Ms. Raff and others, the case seemed clear cut because the companies were armed with data showing how Google had hurt their businesses to help its own.
But the companies struggled to find a receptive audience. In 2013, the Federal Trade Commission decided not to take on Google.