once the Bitcoin is fake it won't have any confirmation from the network and once is a fake Bitcoin transaction it won't include the transaction fee.
There is no such thing as
fake bitcoin or fake transaction. The scam scheme you are talking about consists of sending bitcoin (real bitcoin) to your wallet but the scammer cancels the transaction while it's still unconfirmed. And for this to work, the scmmer needs to set a very small fee rate to guarantee the transaction will remain unconfirmed as long as possible.