body: I'm asking purely out of curiosity, and would be happy with answers relating to any jurisdiction(s).
  
  
  As an example, Ben wants to buy a banana from Sam's shop. Bananas are priced at £0.50 each. Ben puts the banana on the counter and (a) hands Sam a £1 coin. Sam then puts the coin in the till and (b) gives Ben a 50 pence coin.
  
  
  **Was the contract made and completed at point (a) or (b)? Or is the time of sale not legally defined so precisely?**
  
  
  Presumably if it was not made until (b), then Ben might not be entitled to walk away with (or eat) the banana without waiting for change.
  
  
  But if it was made at (a), then Ben might not be entitled to change his mind and get his £1 coin back if Sam was out of change and asked him to wait for five minutes.
  
  
  
title: When purchasing with excess cash in a shop, is the sale completed when I pay, or only when I receive change