I really don't see how this would work, even in RP. Pirates can acquire anything by taking from other people, whether it's demanding cargo or shooting an NPC. What you decide to haul or what you haul it with shouldn't determine how much you make.
On a related note, I have always thought it would be cool if human cargo would be perishable unless hauled by a ship designed to haul people like a liner or a yacht. (this would not include pilots as they would be in escape pods/flight suits, etc.) IRL, if you pack a bunch of people in a cargo box and ship them halfway around the world, there won't be many left when you get there.
In relation to that, you could make certain commodities damage the ship that is hauling them unless the ship is specifically made for that. Like hauling toxic waste. In a regular transport it could eat the hull like exterior radiation, but in a train with hazardous material pods it wouldn't.
