In the fall of 2010, the company did a test. It showed its products two ways—with the video and without the video—to track shoppers' behavior. It found purchases increased about 10% when a product included a video description, says Laurie Williams, video and photo products manager at Zappos. The company is still testing to figure out what components affect sales the most, she says.
Why? A video—even an unflattering one—produces what marketers call "the stimulation process," says Mr. Shiv. When a company shows people an item in action, "your brain is sort of naturally imagining, 'how is this product going to feel on me, how is it going to look on me,' " he says.