In their Inventory, eligible items that have a sellback value and/or not reached the time limit for sellbacks (as per your item configuration) will have a Sell Back button.
Most items will have their effect reversed, but certain things are irreversible (such as Username Changes).
Created forums will not be deleted, since they may have posts in them which would either delete those posts or leave them orphans, forcing you to use the AdminCP vBulletin tool to delete them.