That would be funny... in a bad way of course.
You get to the Coles Checkout and the cashier keeps pulling items off the conveyor and putting them behind her, saying, "sorry, this is out of stock".
You - "But... it's right there! I had it in my trolley. I want to buy it."
Her - "Sorry, the person behind you bought it."
You - "What the? How could they buy it if I had it in my trolley?"
Her - "Don't know, but that's just what happens here. Have a nice day."