Once into the checkout procedure, or at least in my checkout procedure, there's no obvious way to back up, cancel or change the order. At the bottom of each screen, I have "continue" and the Continue button. When you get through these screens, you finally get to PayPal which does offer a "cancel and return" link.

I'd like a "cancel and return" button or link with each step in the checkout procedure. Maybe it's simple, and I just need to turn on this attribute?