Does Groupon have any sort of lock in agreement with its merchants? I've always wondered how these businesses are defensible; apart from negotiated deals, the s

Does Groupon have any sort of lock in agreement with its merchants? I've always wondered how these businesses are defensible; apart from negotiated deals, the services are more or less interchangeable. Groupon's success in San Francisco, for example, doesn't necessarily make it more valuable in New York. Aside from few economies of scale in sales, development and support.