2
A cheque that arrives before you have done anything
The most effective version of the fee scam, because the money looks real.
You win. A cheque arrives for part of the prize. You are told to deposit it and wire a portion back to cover fees or taxes, keeping the rest.
The cheque is counterfeit, but that is not the clever part. The clever part is that banks often make deposited funds available before the cheque has actually cleared. For several days the money is genuinely in your account and genuinely spendable. Then the cheque bounces, the bank reverses the deposit, and the wire you sent is gone for good.
The rule that protects you is simple: funds being available is not the same as a cheque having cleared, and no legitimate promotion will ever ask you to send back part of a prize.