In my latest game I was playing a good civ and there was several neutral civs trying to trade for the good tech concept of righteneous but since they are neutral the tech didn't show up on the trade list but the option to accept the trade was there in effect giving me a free tech from the AI. I ended up getting about 8 different tech from the AI like this and the same AI is still trying to trade for that tech giving me more free techs again and again.
