I'm back at it after an extended break. Today I finished up most of the colony side of the Market system and killed a few bugs with it. Next up is the ship side of the Market which will allow a ship to buy and sell items while landed at a colony.
I think for now I'm going to disallow buying and selling if the ship belongs to the same player as the colony. I don't really see a point in it since ships and colonies all operate off the same money pool for the player.