a boy was at a carnival and went to a booth where a man said to the boy,"If i write your exact weight on the paper u'll pay me $50". If i cannot then I will pay you $50. The boy looked around saw no scale so he agrees, thinking no matter what the man says he'll just say he ways more or less. In the end the boy ends up paying the man $50. How did the man win the bet

The man did exactly what he said. He wrote "YOUR EXACT WEIGHT" on the peice of paper