Implementing something as basic as COD for sending letters is overdue.
Do I even have to explain?
... Just to be save:
You pick an item, put it into the letter and are given the option to set a certain amount of CR or CE as COD.
You send the letter and the reviecer can than pay the amount requested or send the letter back. If he does not pay, he can't get whatever else is attached.
They want you to use auction to sell stuff.
You know, the thing suggested long ago when dinosaurs roamed Cradle so people could sell stuff to other players without having to meet with them.