I use product price modifiers to allow $0 orders if a customer opts to be billed later. The checkout page handles $0 orders well without any customization, however on the receipt page (v1.1) and receipt email (v1.1, v2.0), the payment information lists "Visa" as the payment method. Our customer service department has identified this as being confusing to billed customers since they did not actually use a Visa card to pay. Some people interpret this as them not having to pay because they think a Visa card was somehow used to pay for their purchase, even tho it was not.
The behavior is slightly different between v1.1 and v2.0 and since we have sites using both versions, I have detailed each version below:
v1.1 Receipt Page: Order Information section contains a field "Card Number" with text value "(Visa)".
v1.1 Receipt Email: Order Summary section contains a field "Card Number" with text value "(Visa)".
v2.0 Receipt Page: no problem here
v2.0 Receipt Email: Order Summary section contains a field "Payment Method" with image value showing Visa logo.
By default, orders where no payment was used should list something relevant, like "N/A" in the "Card Number" and "Payment Method" fields, or else do not display these fields at all.