Theme/Plugin for letting users sell predefined (by me) products with their price


I am searching for a Marketplace Theme or Plugin that allows my users to sell products that are added by me for their own price. For Example they have a list of products and can choose what to sell and for what price. But they souldnt be able to create their own products. A good Example is the Website Mmoga where users can sell keys for games for their own price.

Does anybody know something like this?

Thanks in advance!