How to win every coin toss

Okay, here's how you win a coin toss without a double-sided coin. Take a sharp blade and put a tiny burr on the rim. When it's time to flip a coin, take yours out of your pocket, toss it in the air, catch it in your hand, and slap it on your arm. You will be able to determine the side by feel. If your mark guesses incorrectly, pull your hand away. If they guess correctly, you can flip the coin with your thumb quite easily. It may take some practice.