I forget what it's called, but on the "Billing" page, when there's a balance due, a button is presented--called something like, "Pay Amount" or "Pay Owed" or some name that doesn't really imply the "instant" action. Pressing that button causes a default action that uses the Credit Card on file, and completes the checkout process with no "summary" or "review" step.
This month I wanted to take the money from a different account (i.e. PayPal), but I forgot about the default [sudden debit] action (I mean, this only happens once a month, and my memory isn't that good!), so [WAP!] I got slapped with an UnDesired Debit [UDD]!!
Please, either add a "summary"/"review" step between the button click and the actual payment event, or add another option (like Amazon does):
* Option 1: "Instant Pay" [currently, the only option available]
* Option 2: "Select Payment Method"
And, yes, I know [now] that one can access "other payment methods" by clicking the "Manage Payments" button -- but that is UN-intuitive!! That button is not in the "Checkout stream" (i.e. it's outside of the box that contains the Checkout Process, as would be expected for an "administration level" port).