Please Teach Me How To Ruin Your Business!

I work in a small café that also serves rice bowls for lunch. A customer calls in an order that I have ready when she arrives. The following conversation happens:

Customer: “These are so good. Do you ever teach people how to make them so they can make them at home?”

Me: “Um, no.” 

Customer: “Why not? It would be great to be able to make them myself.” 

Me: “It would be detrimental to business if we taught our customers how to make them. Then no one would come here anymore.” 

Customer: “But I have to drive here from [Town five minutes away]. It would be sooo much easier if I could make them myself.” 

All I could do was facepalm.