How can we improve WHMCS?

If I create an admin with access to ONLY one support department that's fine.
The problem is that this admin will also be able to every client etc from that department.
I think there should be an option to also lock the admin to certain client or hide all possible ways of seeing or changing client info.
Also to show or hide other admin users or departments.
We have many resellers that would like to manage tickets but than they would see all clients and all of our staff etc.