Settings-> Users and Permissions
There are two default roles, CEO and manager, where Manager reports to CEO.
Rename Manager to Sales Manager (hover over manager, and click on the center clipboard icon to edit)
Create Sales person Role:
- Click New Role button
- Enter Sales person as Role name
- Choose Sales manager as reports to
- Leave 'share data with peers' box unchecked
Assign roles to the appropriate users.
Also - make sure your Data Sharing Settings (Settings->Users and Permissions->Data Sharing Settings) are set to Private.