You can restrict the roster mailbox so only assigned agents to a specific artist can view the artist bookings on their dashboard. This option will completely lock down other agents to access the bookings. 

This can be managed from the Roster Management Tab. 

You will find two toggles turned on by default:

Agents can manage Agents and Assistants
This setting will let any users from the agency to add and remove agents and assistants on an artist setting.

Agents can view bookings through 'Show Booking'
Any agents can access other agents bookings from the Event stream by clicking the 'Show Booking' link.