Age Detection In The 21st Century

How do you find out if a Co-op shop assistant is over 18? Easy. Put a bottle of booze (any booze) in your basket. Before they put it through the till, if they hold it up and call out towards a colleague, “Alcohol, Martin” and wait for either a "that’s fine", a "yep" or a simple and authorative nod then safely assume said assistant is under 18 years of age.