I want to launch a marketplace site on my niche and I need a good plugin with many functions for that, where users can trade, have their own seller ratings and etc…
WordPress Ecommerce a WordPress Shopping Cart Plugin. One of the best so far for one of my partner’s wordpress sites.
This is the only plugin I am familiar with that may be able to help you -
WordPress › Envato Marketplace Items « WordPress Plugins
I think this is more for the items over at Envato Marketplace…
exoldier, may I know what niche are you in?
Are you sure Wordpress is the best option for this? I’m not 100% sure of what you want - perhaps you could post some links to examples - but in general Wordpress is good for basic ecommerce, membership sites, etc., but if you want something more sophisticated I would look for a different solution.