Just my 2 cents on this.
I tried several "Free" shopping carts in the past 5 years.
Most have gone under. I switched to a host with Miva Merchant and I will never look back.
It is very easy to configure, there is a forum to ask for help besides the company support, there is an open source version you can switch to that has 100's of plug ins to do whatever you can dream up and the language it is written in (Miva Script) is fairley simple to learn to make your own modifications.
You can also write .html pages with the script to do SSI like calls or again anything you can dream up.
This is not a product promotion....I am not affiliated in any way.... I just love the system and the fact that there are only a few people that understand the language.