Most e-commerce sites that I go to have payment information as the last step of the checkout process. Some of these sites provide the option to save my payment info for quicker checkout in the future yet even with these sites, the payment information is the last step before submitting the order.
If my saved payment information is tied to a billing address and I ship to the same address; wouldn't it make more sense to have the payment information the first step in the checkout process and, if saved, have everything else filled in for me?
In some of the user tests that I've done for my clients, most users are similar to my own behavior billing and shipping being the same. I am wondering if anyone knows or has any data indicating why payment information seems to be last in almost every shopping cart checkout process out there. Having payment information first feels more appropriate; however, am curious to know if there's a negative reaction from such or if there's other rationale.
There are some great answers thus far. One thing that I'm attempting to look at is a traditional process which all the answers have been great thus far vs something like Amazon's one-click process where all payment, taxes, and delivery information is already setup and thus make an extremely steamlined processed for returning visitors. While I believe Amazon's one-click checkout process is still patented (or at least was ~10 yrs ago), are there things we can still learn from such?
Updated the phrasing of my question a bit. I meant asking for payment information first in the checkout process and then, if saved, fill in the billing/shipping information and such for the customer. I never meant asking for payment information prior to even product selection or customization.