Credit card reversals aren't such a big problem. They affect your trust and you can only reverse so much until you lose your card and the ability to reverse. A reversable transaction that is not tied to trust is completely different issue.
And that's why I said "determined attacker". A determined attacker would use stolen credit cards.
However, you're correct about casual attackers. Fortunately, since casual attackers wouldn't have a mining farm, they'd succeed so rarely that it's barely worth mentioning.