Prevent certain user roles from showing up in results
For A.

Set up another filter in your view for "User: Roles". Choose the Operator "Is none of" and then, choose in the options the role you dont want seen. You can use the roles filter after the exposed one.

Attached is a pic of the user:roles filter section. The options are cutoff to the right (taken from a working site..want to leave the role names private)



You can also expose the role filter and, limit it to the selections you choose in the options pane.