Assign customers to sales reps/dealers, so they can manage only their customers and create orders for them.
The extension lets you manage access permissions to orders and customers for admin users. Here's how it works: you assign customers to admin users and after that the admin users can view and edit only customers assigned to them; they can view and process orders only of their customers; they can create orders from admin panel only for their customers. Also the admin users can create new customers, who are automatically assigned to them. You can learn more at http://amasty.com/sales-reps-and-dealers.html