Somebody Help This Poor Restaurant: American Express iPhone Coupon

A frustrated restaurateur, who chooses to remain anonymous, asks fellow indie restaurants the following question:

We had a guest present an iPhone coupon from FourSquare at our restaurant yesterday. The deal is “spend $5, get $5 off.” The problem is we never signed up for couponing or advertising or ANYTHING with this company. The guest was very upset when he left. He kept showing everyone the coupon on his phone. He took the $5 out of the waiters tip – and told the waiter he was doing it because he was so pissed off about the iPhone coupon. We took the $5 out of petty cash and made the waiter all good. I’ve since learned the deal is a “Support Small Businesses” program agreement between American Express and Foursquare. American Express will give you $5 off your Amex statement when you log in on Foursquare at these places. Fortunately, we’re on that list. Unfortunately, nobody every informed us of the promotion so we could prepare our employees. Any other restaurants out there having problems with this? Other customers? Thanks.