Unable To Break That Conversational Mould

(I work as a cashier at a hardware store where moulding is sold either by the piece or by the foot. Customers can cut the pieces sold by the foot to their desired length and pay for only the amount they cut. They cannot do this with the ones that are sold by the piece, as it does not prompt for a length to be entered. This story starts with a customer approaching me with moulding that is sold by the piece.)

Me: “Hi, did you find everything you were looking for today?”

Customer: “I have 10 feet.”

Me: *I scan the item and see that it is only sold by the piece* “Sir, this is sold by the piece, not by the foot.”

Customer: “I have 10 feet.”

Me: “This moulding was 12 feet and is sold by the piece, not the foot.”

Customer: “But I only have 10 feet.”

Me: “I understand, but these are only sold by the piece. I can’t enter in a length. You can grab the other bit if you’d like.”

Customer: “I have 10 feet. I only want 10 feet.”

Me: “You’ll have to pay for 12 feet, then, as this is sold by the piece, not the foot.”

Customer: “I don’t understand why I’d have to do that.”

Me: “You can grab the other bit, but I have to charge you for the full piece as this is not sold by the foot and you have already cut it.”

Customer: “But I only have 10 feet!”

Me: “I understand that, but there is nothing I can do. It scans as a full piece.”

Customer: “But I only have 10 feet!” *gives up and pays*

Me: *face-palms*