Infomercials: The one thing you can’t buy is one thing.

In Priceless: The Myth of Fair Value (and How to Take Advantage of It), author William Poundstone writes that the central principle of infomercials is what the economist Richard Thaler calls “Don't wrap all the Christmas presents in one box,” meaning that consumers value freebies that come with a purchased item more than purchasing the same items presented as a set.

“Thaler deduced that marketers should devote less energy to promoting how absolutely wonderful their product is, and more to breaking it down, feature by feature, or selling several products in one bundle,” Mr. Poundstone writes. “The one thing you can't buy in an infomercial is one thing.”

The Snuggie infomercial first plugs the sleeved blanket, then throws in a free book light, announcing the price is $19.95, plus $7.95 for postage and handling, then adds that a buyer also will receive a second Snuggie and second book light for an additional $7.95 for postage and handling. It was compulsory to order two Snuggies and two book lights for a total of $35.85, plus tax, though that actual price was never mentioned. Although now also offered by retailers like Walgreens, the Snuggie is still applauded by direct marketers. In September, Allstar Marketing Group of Hawthorne, N.Y., which markets the Snuggie and other products like the children's toy Bendaroos, was named marketer of the year by Direct Response Marketing Alliance, a trade group.

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