Wondering what e-commerce or CMS tools are good to build it in. I remember long time ago when I did this I used osCommerce (not sure if still around) and Joomla.
Times must have changed since then (2005), what are some open source tools out there?
The gorilla in the room is Magento, owned by eBay these days. Community edition is fine but it's a demanding piece of PHP software built on Zend Framework. Sucks CPU and current version is stuck with MySQL as far as I know.
Lighter alternative is PrestaShop, a French outfit who just secured some lending recently. Probably worth looking at.
ZenCart, WooCommerce plus Drupal with the eCommerce module are in there too.
Just some hints.
I give an idea but you're best off researching it yourself. In terms of overall scalability and capability, Magento is hard to beat. But you have to know a fair bit about the patterns used in it's code base, and know how to code PHP if you need to extend it beyond it's base capabilities. However it's base capabilities are pretty awesome as it stands, and probably has the best range of free extensions, like payment gateways, out of the main open source choices. It is generally thought that Magento demands more server resources. If you look at the code you'll see why. A new version is getting to, or is in beta where other database options like Postgres can be used. Also, a couple of guys that made it are starting a new project for eCommerce but that's a way off.
PrestaShop is a much lighter system that doesn't need as much programming skill, though you'll still need some if you need to go beyond the capabilities it already has. It's themes and addons are part of a large aftermarket, so watch for costs on that. On the other hand you can pretty well run it on a shared server if your scaling suits, at least at first. It's popular as an alternative to Magento, having many of the options you might need like attributes for categories, such as separate pricing per customer. Check the specs though.
Drupal is a CMS with a eCommerce bundle you can apply. Talking about this involves talking about Drupal, and this you'll definitely need to research yourself. It's an appealing way to do things, but you would definitely need to know how to program PHP for Drupal in order to get the facilities you get from the other two I've mentioned.
The other CMS with an eCommerce plugin is WooCommerce for Wordpress. As with Drupal, you'll need to research that yourself. It's main advantage is that it just plugins into Wordpress. It's disadvantages are about Wordpress and scalability. Wordpress is a nice attack target.
There's others based on osCommerce, and others like bigCommerce you can look at.
It's not an easy decision for you. None of them are perfect. I'd just say that the quickest and simplest for a limited range of products with up to a few thousand sales a day would be Prestashop.
If you're going to do a chain of stores or support volumes of products at scale then Magento. Magento also has the ability to publish to eBay easily. Not sure about Prestashop on that.
But don't take my word for it. Get your head around the capabilities and requirements first.
EDIT: Sorry, I didn't see you wanted an open source option.
Just something to think about.