Okay, I will try it a different way. The captain gets a discount, which is based on the pricing of the goods. So, to buy furs at 1350 as an example, he pays 1215 if the discount is ten percent, right? So, you can set up ships such that the price never in the market is below 1300 because they are constantly and continually being bought at that price. These goods are loaded back into your warehouse.
The town needs furs, the bigger the town, the more furs it consumes. It buys them at whatever price it can.
Another ship is continually selling into the market the furs, down to a price of 1300, uploading them from your office. Supply remains steady, but price controlled. And, you are making money as well from your inventory stockpile.
Now let's examine a case.
For an example, consider a town like Memel in the contest. As it grows, you supply it with furs produced elsewhere. It consumes them, at a price you set for sale from your warehouse. You sell at 1300, make several hundred on the sale, times whatever number have been sold. But you have a hundred or more in the warehouse still, idle inventory, and you don't want to dump them on the market. But you want to earn money on this inventory while it otherwise would have been sitting idle. You think about it a bit, and come up with the idea of arbitrage with price manipulation. It is different from the usual type (which relies on town production with or without your additonal production), and generates cash from otherwise unused inventory. Perhaps it should be named Inventory Arbitrage. Lots of goods will work, but for now our example is furs.
So, with arbitrage ships now placed into the town, you buy up furs from the marketplace that you have sold there at a price of 1350 (but you actually have paid 1215, a difference of 1350, put them back into inventory at a discount from the listed market price. With other ships, you sell back into the market. At 1300 selling price, each arbitrage round sale of goods (sold and repurchased) has generated 85 per fur (bought by you at 1215, sold by you at 1300). The town continues to consume furs, always paying more than your sale price of 1300. Supplies are steady. But now the inventory has generated additional moneys and profits beyond those profits you have made from the town consumption. With an inventory arbitrage of just one hundred furs per day you have made 8500. The town perhaps has consumed a dozen that day, which perhaps you originally paid 650 net (including transportation and storage costs) and, selling twelve in total that have been consumed, you made 8400. After taking out captain and crew salaries, your profit is now double what it otherwise would have been.
So is it clear how the price manipulation in Inventory Arbitrage works? You are still providing the town needs, and sell at excellent profits. You have doubled your profit though by putting otherwise idle material to use. In regular arbitrage, you sell hundreds of units at a price perhaps 10 or 20 above the price you paid, in the town that produces the item.
In some of our games, and I will pick on Bizpro here, he has hundreds of units of train oil and leather sitting idle and costing money to store, iron goods too, maybe cloth and wine as well. If he ran Inventory Arbitrage, the town still gets its supply, at a good net profit compared to production, but he makes more money than he otherwise would have made on the otherwise idle inventory.