Bankers can use the shadow government to "take a bit off the top," why not a Steward for their own region?
Evil, but I assure you it happens all too often in RL.
Can't they do this already? Simply make a deal with a trader to sell for a cheap price for a bribe, or set a slightly higher buy order, again for a bribe. There is no button to do this, but the potential is already there.
