WordPress Marketplace is a free full-featured Shopping Cart / eCommerce Plugin with everything you need on an easy UI, to build eShop or marketplace.
I just spent three days and countless hours trying to understand why in the world my site kept returning fatal error after fatal error and glitch after glitch. I tried going through each plugin one by one and narrowed it down to other plugins and took my attention off of WP Marketplace.
Then I remembered reading the reviews for WP Marketplace and how buggy and poorly coded it was supposed to be. So I changed my theme to TwentyFourteen, for which the customization/live preview page would not work for me. Voila! The theme worked perefectly when I deactivated WP Marketplace, and screwed up everything again when I reactivated it. In sum--it's simply a bad plugin--the ones people warn you about when they say it's not quantity but quality when it comes to wordpress plugins...even with a good idea behind it.
I really really really wanted to like this plugin because of all the cool features it lists for free and the fact that all other ecommerce plugins that let users sell are costly. But I never even got a chance to really try it out. Hopefully the developers will re-do the code properly (please let me know if you do), but unfortunately I will have to fork over 100 bucks for premium plugin that doesn't even do half the things WP Marketplace claims it can do.
PS. If you don't believe me, try it for yourself: Install TwentyFourteen theme and try to visit the customize/Live Preview page to edit the theme--Then install WP Marketplace--Then deactivate all other plugins--Next try to visit the TwentyFourteen customization page again...you may notice that you cannot do anything here. Deactivate WP Marketplace and everything works fine again. This is just the tip of the iceberg.
Not sure why this has such high reviews unless it only recently broke. The checkout process is a mess of messy code. PHP errors on a fairly standard install, js errors and a half-finished user creation script. Will be great when it's a little more polished. A word of warning, you'll might need to enable sessions if you're on a cheap host.