It may sounds crazy but at restaurants where I got problematic food(not spoiled, but let's say with hair, or overdone), if the the situation got cleared proffesionaly I went out with a better feeling about the place.
Mistakes happens, I've been on the line long enough to know. The shouldn't but happen. If you give the guest proper treatment, take the dish without arguing, sometimes with an attantive crew without even the guest complaining, he'll know he's in good hands and will return. Make sure mistakes doesn't happen, but always make sure the customer will enjoy himself. Be attantive.