Hello Dave,
Thanks for contacting.
Yes, sellacious is multivendor. Every seller can have your own shop. If a user enters in particular sellers shop "store" he will see only and only his products. our search store module can help the user to search inside any particular store.
Each store can have its own price, discount, tax, coupons etc. Each store can have its own URL example
https://www.yourwebsite.com/store/my-awesome-store
But
as of now, they can not particularly select their design, and store layouts themselves.
Hope this solves your query.
-Abhishek