This idea is for a “customs officer” NPC to be added to trade cities and NPC outposts, where you can deliver captured “black market” crates for less money and more experience than bringing it to the original destination.
This would apply if you intercept a smuggler or pirate who is carrying “contraband” crates like if they took on one of the proposed black market missions. You disable their ship, seize the cargo and discover it to be a shipment of illegal Hibernian pumpkins en route to Creta City, where they would be sold on the underworld.
You now have the option to take the pumpkin crates back to Hibernia and deliver them to the local customs officer who gratefully rewards you with less money than the crates are worth (.4x ?) but significantly more experience, as well as NO BOUNTY.
OR you could play the opportunist route, and make a direct course for trunkadis and deliver the contraband YOURSELF at the (black) market price, incurring the bounty and coming away significantly richer.
This would add more immersion, choices and variety to a unique and interesting trading system.