A great story from MarketingProfs:
At Gina's Pizza and Pastaria in Orange County, CA, the manager asked a customer, "Do you have a coupon? I see you've purchased three of these pizzas in the past few months, and they should have had coupons on the box." The customer didn't.
So the manager took a flyer from the counter and pulled out a coupon. "See, we just saved almost five dollars."
For $4.90, Gina's turned a satisfied customer into a loyal customer. (And got a ton of word of mouth, including blog posts like this.)