What Are the Risks of Using RBF for a Sender or Receiver?

For the sender, the primary risk of using RBF is paying a higher fee than initially intended, although this is usually the desired outcome to speed up confirmation. For the receiver, the risk is more significant, as RBF reintroduces a form of "double-spend" risk before confirmation.

A malicious sender could send a transaction, and if the receiver acts on the unconfirmed payment, the sender could replace it with a new transaction that pays the funds back to themselves. Therefore, receivers should never consider an unconfirmed RBF-flagged transaction as final.