--snip--
But is there someone who has been able (recently) to cancel a broadcasted transaction?
or is it definetely that there is NO WAY to cancel a transaction?
Thus it makes sense to discuss it again.
I have a habit of cheaping out on fees when i move funds between my own wallets. Nowadays, i always opt-in RBF, which makes it very easy to create a double spending transaction with a higher fee and broadcast it, but about a year ago, i did have to create new transactions doublespending the unspent outputs used and input of my own transactions several times. It was during the spam attack and the astronomical fees, and before opt-in RBF was adopted in my wallet, so many of my low-fee between-my-own-wallet transactions got "stuck". doublespending was the fasted way of fixing these problems.
It can be done, but like i said: if you wait for 1+ confirmations, the transaction can no longer be "cancelled" this way.
the question was very tricky just as it covered merchant interest.
when you use fiat refund is a common thing but crypto doesn't have such option.
So, I guess merchants will just have to initiate a new transaction. So, it must have a special system for setting a unique purchase ID and link it to tx id of the payment.