Vendor Login

Example of what I'm trying to implement is like on eBay, when you click on the sell, you don't have to log in again to visit the admin potral, but on cs cart when one register for a user account and then apply for a vendor account when they're approved instead of the admin to be merged to the user account so it can be accessed with just one log in, it will be created in such a way that the vendor has to log in again to visit it as a separate account, how can this be corrected?

If I'm not mistaken, when someone applies to become a vendor, their registered user account becomes a vendor admin account when the vendor is approved.