At the moment customers can register online by themselves, but they all have to pay at checkout. I want to be able to flag certain registered customers who have credit accounts with me at the backend, so that they donâ€™t have to pay at checkout, but I still want to get emailed their order details. Is there any way i can do this?
You can assign a different membership to these customers (e.g., Account). Then you can assign that membership to a payment method - the existing Purchase Order should work.
You will have to let these customers know to use that payment method.