Please point me to some examples, thanks.
So I'm not sure if this is what B3ta is referring to - one solid piece that has gone through a bit of a wringer in terms of testing and configuration/transformation over the years is CS-Cart, which was originally in itself an offshoot of X-Cart.
I believe both carts now have multishop setups. I am more familiar with the CS-Cart edition.
Its a bit tricky, because on some level the owner needs to be able to decide if they want to have one unified database in the backend for various shops (the 'food court') model where you have multiple shops for different types of food but they all share one big common kitchen in the back and also share the credit card processing. Or the subcontract model where each store on the back end has its own unique instance in place with a universal dashboard that allows an admin to oversee everything.
My advice, do not touch it with a 10-foot pole. As much as I love the idea, in practice the coding and debugging required has been a real nightmare/evolution for other products. How deep will admin go? Will customers be shared? Will customers use different logins for each storefront? Do cart contents carry over from one store to another? Do all storefronts have the same shipping and tax rules? Is there a shared pool of inventory that only the admin sees and that sub-storefront admins can pull from? Are products added by sub-storefront owners shareable?
There are just a ton of variables laid on top of the shopping cart platform which already has a tendency to become super bloaty and confusing. CS-Cart made some serious errors during the evolution of their product, it has taken many years for them to iron own the kinks and hurt feelings that multi-vendor has created.
I'd love to see a step up from padloper in terms of interface-in-place. Looking forward to the alphabetagamma.