a GuestLeo , in my opinion, if you want to create a megastore, consider to use CS CART Multi-Vendor
"Multi-Vendor is an extended CS-Cart software that enables you to create an online marketplace where multiple vendors can manage sales of their own products through one common web store." - Price: $1450 www.cs-cart.com/multivendor.html
Joomla Virtuemart Multi Vendor Marketplace|Multivendor For Joomla Virtuemart - WebKul
This remarkable add-on enables the user to convert Joomla Virtuemart store into Multi-vendor/seller marketplace with the concept of single store front.
"Multi-Vendor is an extended CS-Cart software that enables you to create an online marketplace where multiple vendors can manage sales of their own products through one common web store." - Price: $1450
www.cs-cart.com/multivendor.html
Multi-Vendor Shopping Cart Edition of CS-Cart Ecommerce Software Solution
CS-Cart Multi-Vendor Shopping Cart Edition - complete ecommerce software solution for online marketplaces and web shopping malls.