connecting payment with listing that was made by admin?

Hi guys,

I have a new sales rep, and while explaining how to add listings we found no way to connect a payment to the listing.
If a normal client add’s their own listings all is working OK.
BUT
If an admin or a sales rep adds the listing, how do we charge for it?
We can create a user and asign it to the listing but how do we connect the payment?

Also if you have a sales rep, how do you guys work?
Is there a guide out there you can share?

Thank allot for the help,
Eco