Show the Sales Person on Orders and Report for sales per staff
As WHMCS knows who is logged in placing the order (or if it comes via the client directly) , then the Admin user who created the order should show on the report and on the New Order Email.
At the moment you have to check the Client Logs to see who placed the order.
This way a report can easily be created to see the Sales figures per staff member over X period of time. All direct orders from clients can be classed as something like "External" so you can compare direct orders from the website to orders placed by staff.
It also allows staff to easily see who is handling what order for followups internally.