Cart Shopping

I've used Zen Cart in the past - pretty good but I hear Magento and OS Commerce is better. I did install both softwares but never really did anything with them like I did with Zen Cart. source

I'm concerned about using a Shopping Cart that is provided from a host as apposed to buying one or using a free cart. If I use a host provided cart, do I risk loosing it if I change hosts? source

Absolutely right, there isn't much in the way of ready made software that does this out of the box. X-cart gold does have multi vendor capabilities but you need to hack and mod it if you want different interfaces for each customer. That said, one option would be to use it as a base and get special mods written to add the bits that are missing. source

Yep OS Commerce its not problematic unless you make it that way. Out of the box it works fine just make sure you download a stable release or milestone! source

Have a look at Magento and PrestaShop, neither are perfect, but they make a good starting base and both are very seo friendly. Prestashop is easier to setup, but Magento has more back end features and support. source