Angie's List (my company) has created a similar group coupon system (The Big Deal) as Groupon, but targeted to a more niche market. We actually allow companies to set a hard limit on the number of coupons that can get sold. This allows businesses to offer really great deals that they expect may do negative revenue just to bring in new customers, but control the loss with the limit.

I'm surprised Groupon doesn't do this. Or do they and this business just didn't set a limit?