We need two virtuemart hack.
1) Virtuemart to assign groups of buyers and these can be assigned a fee.
The hack is to hide the product category to specific group.
We believe that the hack has to be done in / administrator / components / com_virtuemart / html / shop_browse_queries.php
2) Viruemart to select the view you see the VM admin panel, you can choose between Simple Layout | Extended Layout.
The hack is to hide these options and the Extended Layout view always.
Thanks
