Operations of merchants are controlled with the button at the extreme bottom left of your screen. You can take on a new merchant, give him or her orders or cancel orders, or view a selection of your merchants to check what they are doing.
When any merchant is in a market, you see only his or her name out to the right of the market and cannot see what transporter is being used. Outside a market, however, you see your merchants and your rivals' merchants with their transporters, and you can hover to see where they are headed.
Rivals' merchants are named after their owning families, with a fairly distinctive number, e.g. "Akbar Family #3", but a family can own more than one with any particular number, starting with 1, 2, 3, and 4 but duplicating thereafter. Your merchants have more distinctive names based on the history of the period in which the episode is set. Our page for each episode may list the names, which are the same whichever family you choose.
You can hire a merchant whenever you have enough coins, and they are with you throughout the game at no additional cost. Each time you wish to hire, you see a panel of three (except when fewer than three are left in the pool) with their names and specialties. Highlight your preference and hit the "Hire" button.
Hiring a merchant costs coins. The first one costs 100 coins. Each subsequent one may cost more than his or her predecessor. The increments are not quite the same for all episodes.
For the tutorial game and most of the easy episodes, the prices are 100, 150, 210, 280, 360, 450, 550, 660, 780, and so on, but with a maximum of 1200 and a maximum number of 30.
Each merchant of yours has a specific advantage, and two or more may have the same advantage. The advantage is indicated by an icon below the merchant's name in listings, which is explained in the help text at centre bottom when you hover over the icon. Examples of advantages are "Animal Husbandry", "Honest Reputation", "Price Gouging", and "River Pilot". Some of the advantages are worthless if you have combat disabled.
Merchants follow the routes you order them to, starting at the first stop of a route they have just been ordered to follow. When a merchant has finished business at a stop and is about to move to the next one on the route, you have a few seconds (or unlimited time if you pause the game) to change or cancel the order. If they are carrying commodities at the time, they just keep any that the route requires them to carry away from that stop but wait to sell any that are not required. However, if you then change the route again you may lose commodities with no recompense.
If you edit a route a merchant is on, you are told that merchants on that route will start the new version when their current tasks are finished. This seems to involve not only the leg they are on but also the activities at the next stop and departure from it, which can make for a long period on the old version of the route. If in doubt, stop the merchant at the next stop and switch him or her to a new route that has its first stop there.
The third use of the Merchants button at bottom left lets you display, in alphabetical order, up to four merchants at once (or eight in the "folded" mode) to see what route they are on and with which transporter, what they are carrying, what they plan to buy at the current or next stop, and if at a stop what they are trying to sell. You also see their current credit or debit balance (profit or loss) and you can reset that to 0. Their costs include the costs of switching to more expensive transporters.
Click the scroll bar at right to see more merchants.