A very simple but cnfusing puzzle..!!

. A lady buys goods worth $20 from a shop. (shopkeeper selling the goods with zero profit) .. The lady gives him $100 The shopkeepr gets the change from the next shop and keeps $20 for himself and returns $80 to the lady. .. Later the shopkeepr of the next shop comes with the $100 saying"duplicat e"and takes his money back. . . How much LOSS did the shopkeepr face.? Give answer fast !