Just for the heck of it I tried to buy a resource mine from the Torians. I offerred them a lot of money and they rightfully refused. Several turns later I decided I would just see what it would take, in keeping with the old adage that everyone has their price.
I offered the Torians all my planets and they still wouldn't trade. I had a warm relationship with them and I had the most powerful civ and the most planets.
I agree that the AI shouldn't part with resources easily but FCS it seems extreme to just turn off trading resources completely