The first money you make on Skullduggery Island is by encountering floating "salvage" items (doubloons and cargo), sometimes from ships that have been sunk by pirates and sea monsters. Pick up a few from the sea, but watch out for pirates and monsters that can sink your raft.
When you have some funds, go to the Golden Harbor Bank and borrow more, this will make it easier to accumulate doubloons in a hurry. Repay the loan before it becomes due, and then you can borrow more (up to your total worth).
Avoid losing doubloons (10%) and cargo (10% or 13%) if you are sunk.
You have to sell spices silk and other stuff
To trade and sell on island on skullduggery island you first must be on one of the 5 islands and walk around you should see a post that says " TRADING POST"
You can trade your ship in when you buy a larger one.
Grains, spices ,medicine and silk. Your Welcome
sell and trade with other islands (on one island what ever is cheaper on one island is worth more than the next ).
Simple. There are trading posts at each island all you have to do is sell and buy things from the post.
you sell or you can buy grain, spice, medicine or silk
You go on the island you want to sell on and go to the trading post
anywhere on the map
find broken boats and then sell them
The trader is right at the end of the dock.
go around the islands and trade stuff with then