Drupal Ecommerce store

Im looking to have an ecommerce store added to my drupal site. I want our users to be able to create their own store. List products or services and have them purchased online. They will also get paid after we take a percentage. I want this to be simple to use without a lot of confusing features. I want an upfront price. I would be interested in purchasing an already built system if you have one. Time is of the essence we want this up right away.