I think an interesting idea would be to have a supply and demand system for selling things. for example if everyone is doing order of souls quests at the time it will reduce the price of skulls sold. This could also be set for each outpost rather than all sharing the price.
This would cause players to have to decide weather they want to sell at a low price or risk having loot on their ship for longer to get a higher price. it will also force players to potentially explore other outposts to make the sale for a better price. It would also make players do other types of quests so they have more variation as ONLY doing say Merchant quests by the time you sell half your loot you will not be getting as much.
This could be down to individual items or just type of item. They could use the price range already introduced for each item.
