Over the Sea and Far Away
Silver and copper coins are the currency of the Colony. Gold, artifacts and other materials are severely restricted. If authorities discover anyone with them, they are confiscated “for the crown”. The governor and military officers are intent on squeezing as much wealth out of the Colony as possible, so there is a brisk underground trade in these commodities.
Black Marketeers within the Colony will exchange gold and some gems for SP at about a 10% return (so 100 gp will be worth 100 sp). No transactions can be made in gold.
A friendly fence might up this to 15%, but basically nobody in the Colony can move art objects, gems or artifacts, for fear of the local authorities. Markets in the Free Ports can exchange those goods at about 20% return, and can actually move these materials.
Pirate fences will move basically anything, but there is a good chance that the crews in charge of the port or the fence will simply attempt to kill the party.