You can restrict user's access to some selected groups of vehicles only. For example, you could create a few vehicle groups and associate them with departments in your organization, like "Shipping", "Sales", "Production", etc. Then you could enable your sales manager to only access the vehicles that are associated to the group "Sales".
We encourage you to read this article to learn how to create and manage "Vehicle Groups".
Associate Vehicle Group(s) with a User
Before you can associate vehicle groups with a user, you have to make sure this user is configured so it can only access "Allowed vehicle groups", and not all the vehicles. So navigate to "Security - Users" view:
As you can see in the following list of users, user "Joey Gonter" has access to all the vehicle groups while user "Jon Doe" is configured so it can only access allowed vehicle groups (no vehicle groups are associated with this user yet, so this is why you see "0 (Edit)" in the "Allowed vehicle groups" column):
To change this behavior, double click the user so the Edit form will show up, then check/uncheck this box:
To allow "Jon Doe" to access one or many vehicle groups, click "Edit" in the "Allowed vehicle groups" column, then select the vehicle group(s) you want to associate and click "Save":
That's it, "Jon Doe" will now only have access to vehicles that belongs to the "Sales department" group.