FAQ - Commerce

1. My houses say they need food. How do I provide it to them?
First of all, you need to produce food in farms, or hunt animals, or fish, or import food. When you have some food, you need to store it in the mill, build a mill not too far from your housing blocks. Now build a market square close to your houses, and build a food shop on top of it. If the food shop gets employees, you'll see a market lady go to the mill to return with food. Once the market has some food to distribute, it sends out a peddler, which 'sells' the food to the houses he passes. Your houses now have food and will probably upgrade to a higher level.
2. My houses need plain/appetizing food, what's that and how do I provide it?
Plain and appetizing food are foods which exist of 2 or more different food types, see this page for info on the different food types. To provide such food, you need to have one or more different foods in ONE mill. Right-click on the market square serving the houses, and set the 'minimum food quality' to plain or appetizing (whatever your houses need). The food buyer will now only get food that is at or above the food quality you just set.
3. Traders don't sell anything to me.
I assume you've already built a trading station/quay to the city you want to buy goods from. First thing to check then: does the trading station have the workers it needs? An understaffed trading station will not be able to buy and sell goods. Second thing to check: is the price of the goods higher than you are willing to pay for the goods? If that's the case, the price will be listed in red when you right-click on the trade post. To up the price you are willing to pay, open the distribution full report, and adjust the prices by clicking on the arrows next to them.
Last thing you may want to check: is the city still trading with you? Sometimes cities will just stop trading with you, but if you've already built a trade post, it will stay there, but no traders will ever arrive.
4. Traders don't buy anything from me.
As with the previous question, check if the trading station/quay has enough workers to be able to sell goods to other cities, and check if the city is still trading with you.
Do you try to sell them goods at a higher price than normal? If that's the case, the price will be listed in red when you right-click the trading station.
Also check if you aren't stockpiling the goods you want to sell: see more on stockpiling in question Commerce#7.
5. I have a warehouse getting goods and a trading station, disconnected from the rest of the city, but the trading station remains empty.
Let's clarify the situation: you're trying to sell [random chosen good] stone to another city. You have a tradion station somewhere in the open, disconnected from the rest of your city (and the stone), and you try to get the stone to the trading station by using a warehouse getting stone right next to the station. Some time, you notice that you have 32 stone in the warehouse but you aren't selling any stone.
This is a little 'inconvenience' in the game: a trading station won't get any goods from a 'getting' warehouse, you have to manually turn the warehouse back to 'accepting' stone, then the trading station gets the stone from the warehouse to sell.
6. My market square refuses to buy hemp/ceramics/whatever while it's in a nearby warehouse and my houses devolve. What's wrong?
The biggest possibility is that you accidentally stockpiled those goods. See the question below for more on stockpiling.
7. What is stockpiling? How do I 'unstockpile' goods?
Stockpiling a good means no one in your city will use that good until you turn stockpiling off. You may want to do this to get enough goods in your warehouses to meet a request. Setting something to stockpile is easily done by accident, because you only have to click once on one of the goods listed in the Commerce tab to stockpile it.
To stop stockpiling a certain good (and checking if you [accidentally] stockpiles something:
Click on the Industry tab (the third tab from the top) and check the list with goods there: if something is listed in red, it means it's stockpiled and won't be used by anyone, including markets, industries and trade. Click on it to stop stockpiling it.