All free for one customer, how to ?

Dears,

zencart 1.3.9
I'm selling to other shops, in this case, they pay for what they order at the end of the month, not right when they order.
Now I would like them to order online instead of calling me, so I would need an option so that they can order without going through the payment process but still I need the Invoice and packing slip to be complete with all the infos (prices, tax, etc...).
If possible I would like to enable this option for certain emails (cf the emails of the owner of the shop to whom I'm selling).
How to do that ?
If you have any idea ... thank you

The Check/Money Order payment module will handle this. You could customize it to check the logged-in customer's id against a list of allowed ids before displaying the option for this.
Customizing the text to explain the process for using it once active is done by editing appropriate language file defines.