Cash on delivery via mail would be wonderful. Having to be WITH a person to trade somewhat stinks. I'm actually quite surprised there is no COD as of yet.
I like that NOT having it encourages people to trade in person.
Yet I am not opposed to COD selling. The trader achievements would still exist but COD would not count towards them.
It would be nice to order food for delivery from the yet to exist MARKETPLACE CHAT from a chef who is cooking it up fresh instead of buying that stale stuff from the auctions. That way I can order exactly as many or as few as I want instead of being restricted to whatever lots are available at auction at that time.