A woman in a shoe shop pays for a £30 pair of shoes with a £50 note. The salesman doesn't have enough change, so he goes to the shop next door to break the £50 note, returns to his shop and gives the woman her change. A while later, the shopkeeper from next door storms into the shoe shop.
It turns out that the note he gave her was a fake! The mortified shoe salesman gives the shopkeeper £50 from the till to apologise. Neither the customer nor the shoes she took are found.
In total, how much did the shoe shop lose?