Maybe I missed something, but I've traded techs and resources without open borders on the diplomacy screen. Sure, I take a commerce hit on the foreign trade routes, but that may be a bigger hit if he could actually foist his money-grubber on me.
I doubt anyone would spread a corp who didn't own it, seems silly to profit one player in exchange for messing with another (if it is messing, the person you're attacking may like the exchange of money for benefits and paid for the privilege).
I just want to keep free market/environmentalism without fear somebody will make me pay through the nose.
the international trading stops i.e. trade routes iirc. I could be wrong though since im still in the infancy of playing BTS.
I propose that you should spread a corp you don't own, to anyone but yourself.
Imagine this if you will: someone spreads a corp you dont want and you dont own into your one cities. Take this as an opportunity to create as many execs as possible under mercantilism. this prevents a further spread of the corporation you don't want in your city while making the payments for the corp as small as possible. step two is sending all the execs you've created through whatever means and sending them back to the original civ that owns the corp. then you settle these execs anywhere and everywhere within the owner's territory. after that is completed go state property and create as many espionage points as possible. use spies to destroy courthouses in whatever city has a corp. this hurts them severely.
so if theyre still running free market then theyre screwed, if they go mercantilism they are totally screwed, and if they go state property they arent going to spread their corp any further and you can revert to whatever plan you had.