If there's a Tarsnap outage because I screwed something up, I give Tarsnap users a credit to their accounts... without waiting for them to complain.
Apparently this is unusual. I can't imagine doing it any other way; I mean, who wants to deal with thousands of emails from customers who are owed account credits?
I got an email last week that I had only $ 0.115755044102126754 left in my account. The last time I paid was $10.00 in June 2015. I'm guessing that I'm fairly representative of most of Tarsnap's customers; for $10 charges once every year and a half recurring billing seems a bit silly.
Storing credit card numbers is annoying (unless you don't care to do it right, but it's pretty clear he does care). On the other hand, there are payment processors that will handle that sort of thing for you, for a fee.
Typically you're going to be storing tokens from e.g. Stripe these days, and not raw cards. Major card carriers provide the same service too. Still worth doing well and securely, but much less risky
Apparently this is unusual. I can't imagine doing it any other way; I mean, who wants to deal with thousands of emails from customers who are owed account credits?