The AI is extremely reluctant to trade stuff. Apparently, it won't trade at all unless it get things at outrageously good prices. Now, I would like to know whether the AI's is equally reluctant to trade in-between or if it's only with the player. In either case, I think the AI needs to be changed. Trading techs and more is extremely helpful (if you trade with three players you only need to research one fourth of the techs you would otherwise have to). The AI should look to get a good deal but currently it is just too reluctant to trade.