Jedoc

I don't think I've ever been able to get an AI to sell me a mining starbase, although honestly it's been a long time since I tried. I usually end up with most of the resources by the end of the game by the simple expedient of parking miners next to rival starbases and checking every few turns to see if any have been destroyed. Plus, when a civilization is destroyed or surrenders, all of its starbases vanish, so it pays to have a constructor in the neighborhood to snap up the suddenly-available