The thing is that every card has a limit, both regular debit and credit. You can easily have a bank account with no more than a couple dollars in it and DO woul

The thing is that every card has a limit, both regular debit and credit. You can easily have a bank account with no more than a couple dollars in it and DO would accept that just fine. If you haven't preauthorized, you aren't guaranteed payment. That's why these services also have usage limits, of course--AWS doesn't want me to rack up a million dollar bill without seeing a past payment history that would indicate I can actually afford that.