I have worked with quite a few checkout systems and eCommerce platforms. Are there certain kinds of interfaces that convert sales better than others?
For me there are really only two questions:
SSL self hosted vs. 3rd party checkout
for SSL this requires an SSL certificate and secure website routines to handle a credit card.
for 3rd party, there is PayPal, Authorize.net, and GoogleCheckout
Single-Step vs. multicheckout see: step two on this page
Single-Step seems easy enough, but does it convert better?
multicheckout can get convoluted, but with a progress bar does it help the user convert?
Hopefully this will focus on the four possible answers given either/or answers to the above.