I was in Cape Town

Last week I was in Cape Town for a few days. For any shopping had to be paid in the national currency, I went to an Exchange Office. At the Exchange Office started the conversation:
– Hello. I want to exchange 40 dollars
– No problem but as you know, our fee is 20%. May want to change?
I thought a little and I answer:
– Not now. I come back when your fee will be 100%.
I left the Exchange Office. In the back I heard the office girl as was laughing in the roar.