I personally almost never tech trade, or piddle with the AIs for money or war.
This is mainly because I can never fathom how the AI is valuating a trade. I can understand wanting to have the better end of the deal, or not giving away valuable techs.
The strangest valuations to me are for trade goods. Say I have vr modules, or ultra spices, and I try to sell them to another civ. Often the AI won't offer any more than 200-300 bc for such a trade good.
If you think about it, a 10-20% morale bonus is worth a hell of lot more than 200-300 bc. That morale bonus should allow them to raise taxes, and make more money. Taken over hundreds of planets, over the rest of the game, that is a huge advantage. And yet the AI will only offer 200-300 for it? Why? He's not really losing anything. I would be happy with 1-2k, even though it's worth a lot more than that.
Is this because the AI was tuned to play a small galaxy, or am I missing something?