How can someone reverse Bitcoin payments?

You can reverse unconfirmed payments in the chain. Transactions that spend the same previous output will send those same funds to an address owned by the sender, and therefore can “reverse” or “cancel” payments. It does not cancel because it does so using another transaction. Replace the payment with another payment. note that RBF Minors can choose what to include blocks and so you don’t need to receive a signal to do that Full RBF Some have been the default policy since the last Bitcoin core release.

Once payment is confirmed, it will no longer be possible to reverse “voluntarily.” In the case of a block reorganization, if the transaction becomes unconfirmed again (along with its descendants) it can be reversed. This chance decreases with passing time and adding blocks above it.

Consider this is a distributed network. Miners are free to add the transactions they need to block, even if they try to replace it with another transaction, to pay more. You can see if the first version is mined even if you exchange transactions. Or, even after Reorg, the confirmed transactions are different.