First make sure the Docks district is Sanitized i.e. finding all citizens and make sure they are not sick. Then go to the Western Docks and Find Martin Nightingale and ask to trade with him. You'll notice that the price for his good doesn't appear meaning it's all free. You can still get money from selling your items to him. Sell off everything you have (Ingredients would work the fastest) and "buy" them back. This can be done repeatedly until satisfied.