Agents Commission condition Type ( Outside sales agent as Cust / Vendor)

Dear Brothers,

I need to configure "Agents commission" as a condition type in Sales order Pricing and Sales Invoicing ,Where in i can pay the commission to the outside agent after the sales invoice is done for my customer .

I think if it is our own company sales man we can do it through partner determination. but if it is an outside unknown person or agent or customer or vendor who is bringing sales to my company and iam paying him the commission how can i do it how can i give him commission and show him in SAP.

Please let me know the method to configure it in detailed Steps...

thanks in advance

Mansur Ali khan.