Not In Receipt Of Common Sense

I’m in line behind a customer who’s buying a battery.

Cashier: “Do you want your receipt?”

Customer: “No, thanks.”

The cashier throws the receipt away.

Customer: “Do you guarantee your batteries? What do I do if I install it and it doesn’t work?” 

Cashier: *Fishing the receipt from the trash* “That’s why I asked if you wanted your receipt.”