This offers a comprehensive List of all trade goods aswell as their best and worst Prices. Pick the right trade goods, buy near the lowest and sell at the highest price. Guaranteed to get you big bucks.
To use this table successfully you should make sure to pick the right trade goods initially. For said selection I included the Delta and Factor of the prices. If weight is no constraint for your party, pick the trade goods with the highest Deltas. If you want to operate the most weight-efficient, pick the trade goods with the highest Factors.
No matter what you do, don´t pick trade goods with neither a high Delta nor Factor. Also don´t buy at more than the "Max Buy" price and don´t sell below the "Min Sell" price. Ideally you want to be as close to the extreme ends of the price ranges as possible.
If you have a big party also keep in mind that expensive food you want to trade might be eaten up by your party while you keep searching for a city with good selling prices.