Complex negotiations involving Trade Goods are obviously a pain in the neck for AI (in ToA, at least).
For example, during negotiations I offer three techs in exchange for Economic Treaty. AI refuses (and rightly so). Then I offer the SAME three techs and ask for Economic Treaty AND Xinathium Hull Plating in return. AI all of the sudden agrees, although this is a far worse deal than the previous one which he refused. I play as Terran Alliance, with huge diplomatic bonuses, but this is obviously a bug, not my diplomatic "skill".