It would be great if sales agents could only see their personally entered data.

We can do this through filters but there is unnecessary mess when a new agent can see everyone contacts, properties and listings.
Ideally each user would only see the data they have personally entered and this could be done easily with a privilege setting. By only seeing personal data you could watch your database grow with relevant contacts that you have met or entered personally.
This would prevent agents marketing to others databases and allow new agents to build relationships with everyone they meet.