To calculate market cap, you take the most recent trade and multiply it by the total number of coins/shares/etc that exist. Since the number of coins is decided

To calculate market cap, you take the most recent trade and multiply it by the total number of coins/shares/etc that exist. Since the number of coins is decided by the coin's creator, all they need to do is sell a single coin for a single cent to get whatever market cap they want. Furthermore, scammers often do "wash trades" where they set up two accounts and have one purchase from the other, for whatever price they feel like. So now they're making up both of the numbers that get multiplied to determine the market cap.