Someone asks about this every few months. You can contact me by email if you'd like to discuss getting a custom component built for this, but you should understand it's a much larger job than you might think. Integration of a payment processor (like paypal) alone is quite an ordeal. Then you have to consider how you are going to handle disputes. There are a lot of different things to consider.
For example, here is one topic about it from a few months ago: https://www.opensource-socialnetwork.org/discussion/view/3372/marketplace-shopping-component-for-ossn