Buy-one, get-one offers are a tried-and-true discounting strategy. But Domino’s found a way to use this idea to build traffic. The company’s “Emergency Pizza” promotion last year gave customers a free medium two-topping pizza. But customers had to come back again. It worked. The chain’s traffic turned positive late last year into this year. CEO Russell Weiner called it the best buy-one, get-one offer of his career.