While there is still plenty of room for improvement, I think things are at least sometimes better than described here. If you are friendly with them, you can get good deals for them - in fact, often too favorable. An allied civ will frequently give me 3 luxes and only require 2 luxes in return, sometimes I even get 2 for 1, which feels a bit like taking candy from a baby. Open Border for 1 gold (not 1 GPT, but 1 gold) needs to be fixed asap., clearly the AI (or developers) do not understand the value of this early game.
When they are unfriendly, obviously the give you worse deals. At least I feels they don't come nagging with stupid offers as often as they used to. Sometimes I sell strategic resources under market value if my stock are full. Why would I not sell 20 Iron for a couple of GPT to an AI sitting on another continent, unless perhaps if I can see they are starting to steamroll? I'm not so prone to selling off extra luxes undervalue, but I can see some rationale in it still, if you're not planning on expanding yourself.