Critically, Google demotes a sponsor to a lower rung on its page if its response rate is too low, elevating a rival's ad for getting more clicks.

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And they're looking into allegations that Google unfairly takes information collected by rivals, such as reviews of local businesses, to use on its own specialized site and then demotes the rivals' services in its search results, the people said.

WSJ: FTC Focuses Google Probe on Android, Web Search