I am working with a client who is doing a multi-phase project. In the next phase, they are wanting a way for users (who are in a group) to be able to list and sell products on their own. Some products would be available only to those in another group, and other products could be bought by anyone.

From what I can tell, no such addon exists for the core commerce package.

Any suggestions on how to set something like this up. OR... is there someone willing to build an addon for the marketplace that can do this?