One of the pains about buying stuff online in the US is that they are a day behind us, and the banks credit stuff on the DATE paid rather than the actual time, so, if I work out how much I need to pay, put it in my low interest account, and then buy it. Unfortunately, that means that I put it in on 20/12 (my current date), and the charge from the US is 19/12 (probable US current date), so I have overdrawn my account (actually I haven't because it didn't happen that way). And of course, if I go through the motions, I don't know how much it will be until I have got halfway through paying, and they have worked out how much the international postage will be. So, I need to almost finish buying something, stop, move the money, and go back the next day and order again. Absolute PAIN.
Anyway, the first time this happened and I got a "overdrawn" fee, I rang up to complain, and the person waived my fee, explained very nicely why it had happened, and advised me how to stop it from happening.
Of course, I could use a credit card rather than a debit card, but then I would open myself to all those internet fraudsters.