My guess is this sounds more like a marketplace type environment where when you checkout, you just "pay" some mystery main store, and each of the individual stores which was selling an item ship their own little piece. Sorta like on Amazon, you can have stuff from more than 1 seller, checkout, and all the stuff is there and you pay once. Those individual sellers then just process their part and get paid individually from Amazon payments.
Downside with this I've seen having sold on marketplaces for years is customers get "confused" who they bought it from. Some people were verbally abusive to me stating I ran all of Etsy personally when they bought something from something else (not even my sale).
I believe some people here would like a "marketplace" environment/option however and the devs might be working on this...
Not so important for me personally however.
Magento is very expensive to deploy from what I've read/researched...18k/year from an article I just pulled up. They have a free one, but seems severely limited. No caching on page (useless slow then), no built in security, no promotion options...just a quick few...