Abilities:
Heres how the Banker could work, if you captured someone's mine his global ability would be you gain 50% of their lossed Neptunium so basically 10% of their current total.
If the Banker is on a mine he hides the total Neptunium that the mine produces. Could make funding a little harder to guess if done at the right time and make a nasty combo with the tycoon.
The game is meant to involve misinformation after all could add another sneaky way to keep ahead. Assuming people don't have eyes on your mines.
The global ability could stack so with two Bankers you take 20% of the someone's Neptunium.
Drawbacks could be (Doesn't have to be all of these) :
The Banker 1 in 5 chance of keeping 50% of the profits for himself. This means you would always gain at least 5% of someone's Neptunium while having a Banker.
He must be on a Mine for his abilities to work.
If caught in transit he changes sides straight away. The Banker changes ownership if captured on mine/outpost or factory.
That seems like a lot of rules but I'm sure he could be simplified or summed up faster. What do people think? =)