WP-Ecommerce has three stars because the owner (who isn't a developer) aggressively marketed the plugin and left it's users hanging out to dry. Updates were done by several hired developers who ended up making a mess of the code. Anyone who wrote a negative review about it was met with an abusive comment from the owner.

This was two years ago since I last tried the plugin so I don't know how support is now, but the way it's written is unsuitable as a reliable ecommerce platform. I tried to set up a jewelry shop for a client who had bracelets in different colors and designs. It wasn't until the website slowed down to a crawl that I found that the system created 30 bracelets x 8 colors x 15 designs = 3600 records in the database. Every time you tried to update a price all 3600 records needed to be updated. And as most people know doing anything 3600 times in WordPress is a pain.

Woo-commerce and MarketPress are much better, but at the moment there are no good e-commerce solutions for WordPress. WordPress has become decent for use as a CMS but if you're looking for an e-commerce solution your best bet would be a stand-alone system like OpenCart or managed like Shopify or Magento Go.