Now as someone who has worked retail, usually (not always) it’s because there is a line (some arbitrary number between 3-6) that is too many people in line. So we take you to the next one. But you only need one person to run so many self checkout machines. Typically 4-6. As for the coupon. That is probably the one time she’s really allowed to tell a customer no, when typically she has to honor more or less whatever a customer tells her to do, no matter how stupid.