When my youngest does the wrong thing in the supermarket (usually while i am paying at the register) I ask the checkout person to 'have words' with him. They usually are more than happy! "You listen to your Mummy! I'm sure you won't climb on the shelves next time you come here will you?" DS quietly shakes his head LOL

People need to make use of their village more often, kids are faaaar more likely to listen to a stranger than their mum ... i find it works a treat!