I agree that I am going beyond the call of duty. In most cases I do ask. Sometimes it's the food, other times it wasn't what they were expecting or they just ordered too much food. I would rather take the food off their bill and have them walk out of there with a good dining experience rather than feel like they've paid too much for food they didn't eat. If I were in a restaurant and the food was inedible I would not pay for it. If the server didn't take care of the problem than I would go right to the manager.