Small business means you can't / don't want to regularly pay to a programmer to customize the cart, right? Open Source is no way then. It's made by programmers for programmers. For example, ZenCart's backend is just a maze IMHO... I can say that because I worked with Avactis
shopping cart and really enjoyed it. It's usable, and easily skinnable. Lots of payment options, too. Take a look yourself.
Though your avatar tells that you like to hurt yourself... so maybe ZenCart is right for you LOL
