Pepsi twice ended up in court after promotions went disastrously wrong. Other big companies have fallen into the same trap - promising customers rewards so generous that to fulfil the promise might mean corporate bankruptcy.

Businesses and customers alike are sometimes blinded by the big numbers in such PR stunts - but it's usually the customers, not the businesses, who end up losing out.

Read more about Tim's work at http://timharford.com/

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