May not be entirely Saino's fault - I've seen people swap the contents of their baskets for the reduced items, leaving the full price item on the reduced shelf.

This kind of behaviour is possibly also partially to blame for the stinky chicken - customer takes chicken out of chiller, wanders around shop for indeterminate time, with chicken warming up, changes mind at some point and abandons chicken, possibly at the till, but could be anywhere. It then takes another x hours for the chicken to get back to its place in the chiller, during which it's thoroughly warm and a breeding ground for all sorts of nasties. Sainsburys should routinely bin any item found out of its chiller.