A customer of a crutch shop bought a crutch made in 30 yuan. He took out a ticket for 50 yuan and asked for change.

Just as there was no change in the store, the shopkeeper went to the neighbor's house to change the ticket for 50 yuan and gave the customer 20 yuan's change.

Just after the customer left, the neighbors came running in a panic and said that this ticket for 50 yuan was fake. The shopkeeper had to compensate his neighbor 50 yuan. Then I went out to chase the customer, caught him and said, "You liar, I paid 50 yuan, neighbor, and I gave you 20 yuan. You took a crutch, and you have to compensate me 100 yuan. "

The customer said, "The cost of a walking stick is 30 Yuan You left when your neighbor gave you change, so I only took your 70 yuan."

Please calculate, how much is the real loss of the rattan shop? I would like to add here that the cost of crutches is 20 yuan. If this customer succeeds, how much will * * * cheat?