A Tricky Salesman
A man walks into a shop and finds an item he would like to purchase. He takes the item up to the salesman. The salesman tells the man "Sir, I would like to make a wager with you. On this paper, I will write your name. If I am wrong, I will let you have that item for free, however, if I am right, you will have to pay double for it." The man thinks and decides to take the wager, after all, there is a very small chance the salesman would actually know his name. In the end, the man walked out of the store having payed double the price for the item. Why?
It's another play on words.
The salesman simply wrote "Your Name" on the paper.