We have just deployed improvements to your checkout flows that allow you to better manage offline payments, and offer multiple payment options to your clients.
First, we have created an "offline payment processor" that makes it clearer for your clients how they can pay offline. It also notifies you when a client chooses to pay an order offline.
In addition, you can now have multiple payment options displayed on the payment page. For example, you can have options for Credit Card payment, Paypal, Checks, or Bank transfer / wire.
And as before, once an offline payment is received, a single click on "Mark order as paid" in your admin space will initiate the automated delivery of any licensed image file present in the order.