Customer Service Case Study "No Substitutions"

I went to a family restaurant, ordered a sandwich and asked whether I could have chips or coleslaw instead of potato salad as a side. The waitress said in sort of a gruff voice that no substitutions were allowed. After waiting an unusually long time for the food to come she finally brought our meals. The plate with the sandwich I had ordered had fruit on the side. I asked why and she said that they ran out of potato salad and had to substitute. ???