Mulla Nasrudin

Tit for tat

   Nasrudin went into a shop to buy a pair of trousers. Then he changed
his mind and chose a cloak instead, at the same price.
   Picking up the cloak he left the shop.
   ‘You have not paid,’ shouted the merchant.
   ‘I left you the trousers, which were of the same value as the cloak,’
   ‘But you did not pay for the trousers either.’
   ‘Of course not,’ said the Mulla — ‘why should I pay for something
that I did not want to buy?’