How Does RBF Influence the Security of Zero-Confirmation Transactions?

RBF significantly reduces the security of zero-confirmation (0-conf) transactions, which are transactions not yet included in a block. With RBF, a sender can easily double-spend by broadcasting the original 0-conf transaction and then immediately replacing it with a conflicting transaction that pays the funds back to the sender, with a higher fee.

Merchants accepting 0-conf payments are therefore at a higher risk of fraud if the transaction was flagged as RBF-enabled.