I have been theorycrafting a bit and doing minor experiments in a turn based game. It seems that you can generate money out of thin air by doing the following:
- Have a planet with at least 51 Resources and no Industry.
- Have at least two players in proximity of said planet
- Build economy 1 (cost: 9$ or less) on said planet.
- Have ships from alternating players loop, so that the planet changes ownership every tick.
- Rebuild economy 1 every tick.
This will generate various amounts of money, depending on the resources and terraforming levels involved, as destroying economy yields 10$ per level destroyed.
Of course, there is only a very short period in the game where this strategy actually yields more than just having economy built on the planet, still I believe this is not intended.