Original Post by Lancer27@impressions
First, let me say that I completed every scenario in the game prior to its release, have grown cities in excess of 18,000 population and have built city blocks of 8 luxury palaces in every scenario with the commodities to make this possible. I don't build long roads with no intersections, I build normal city blocks (Megalord describes my cities as looking like New York). For markets, in a city of 10,000 people I'll have 23 markets: 5 for each of 3 population centers of mid-level housing (200 tiles of housing per population center) and 8 for my palace block of 8 luxury palaces (since palaces require more commodities, market buyers need to make more trips to more different granaries/warehouses). I don't have any trouble with either 'Market buyer' walkers or 'Market trader' walkers.
Given the number of complaints, it is clear that either there is a problem that I am not seeing or that the source of the frustration is due to a lack of understanding of how the market walkers function, leading to either misplacement of markets or the granaries/warehouses where they get their supplies. I strongly suspect the latter, so here is a detailed explanation of how market walkers work in the hope that it will help you relieve any problems you are experiencing in getting them to do what you want.
Each market puts out 2 walkers, a 'market buyer' and a 'market trader'. The 'buyer' goes from the market to a granary/warehouse and returns with goods, carried by little boys each of whom will carry one cartload (100 units) of a particular good. Market buyers will only buy one commodity at a time. They will only buy commodities that the 'market trader' from their market needs to distribute (based on the needs of the housing that they pass by). Market buyers do not wander: they make specific trips to specific warehouses/granaries that have a supply of the commodity that they need to buy next. Market buyers have the same graphic as market traders, you can tell the difference by right-clicking on them to see if they are a buyer or a trader, you can always spot a buyer if she is followed by a line of boys carrying her purchase, or you can usually tell by their behavior.
Important things to remember with 'market buyers' 1) It is highly important to keep the warehouses/granaries that the market buyers must walk to within easy reach of the markets. Otherwise the market buyer will spend an inordinate amount of time walking across the map to a source of a particular good and by the time she returns her market will have been completely emptied by the 'market trader' distributing stuff to housing. In this case, the 'market trader' is left spinning her wheels: she keeps walking around but her source market has no food/goods so she is not distributing anything to the houses she passes. Click on the various markets to see what they contain. If you need to transport food/goods across the map, do so by using warehouse/granary 'Get' commands, don't make market buyers travel too far. 2) Since 'market buyers' need to make a specific trip to buy each type of good needed by the housing its 'trader' passes, the higher the level of your housing, the more trips the buyer must make. The quickest way to avoid trouble here is to use twice as many markets for villas/palaces as you use for casa/insulae level housing. This will help insure that if a particular market is currently lacking 1-3 commodities of the 7 needed, another nearby market will likely have those commodities. Since buyers buy what is most needed, this will not be a static situation. Also, this problem is worse when housing first evolves: the houses have no supply of a particular good and therefore have a high demand for it. Once they are supplied with it, their demand decreases. I think of this as filling up the pipeline. For example, when your housing first reaches Grand Insulae level, they have no wine. The markets they are supplied from likely have no wine. It takes awhile for wine to be given to all of the houses and you may see some devolution in the meantime. Once they all have a good supply though, they only need to replace what they use and the 'trader' needs to deliver less and eventually the buyer has bought enough to fill up both the houses and the markets with a large supply. 3) Market buyers choose their destination when they set out from their market, based on what they want to buy and the quantity of that item in your warehouses/granaries. If multiple market buyers are drawing from the same source, it may happen that the source is dry, or nearly so, at the time the buyer gets there. She'll buy whatever's there and return. I don't believe there's a specific limit to how much they'll buy, they will return with at least up to 8 'boys' carrying one cartload apiece and I've since 12 or 13 boys on occasion. There are a couple of things you can do here: ensure a bountiful supply so that the warehouse/granary is more likely to be full when the buyer gets there and, if you are overproducing, pop up a few extra granaries/warehouses to receive your surplus: some market buyers will draw from one while others draw from another and, again, they will be more likely to find more to buy when they arrive. If I have a large area of farmland supplying a granary that has either a large number of 'Get' carts drawing from it or a lot of market buyers drawing from it, or both, I find it much more effective to build 2 or 3 such granaries instead (since each 'get' cart or market buyer takes a large amount, it is possible that the next to arrive finds an empty granary even if you are overproducing). Ditto for warehouses. Market Traders are like other access walkers: they don't have a set route and they don't have a specific destination. They use the same algorithm to randomize their route at every intersection (the algorithm makes it highly unlikely that they will repeatedly follow the same route). Market traders distribute food/goods to housing that they pass by, as long as the housing needs that type of food or that particular good for its current level of evolution or the next level above it (so it will be given what it needs to evolve, but not things needed several levels above: to prevent waste of food/goods by housing that you don't want to evolve). Market traders report back to their markets the needs of the housing they pass, so that buyers will know what to buy. Each market trader is associated with the specific market that created her: she can only deliver items that the market contains (the market contains things that have been brought to it by its buyer). Unlike buyers who buy one commodity at a time, a market trader will deliver up to 8 different items to every house she passes (assuming her parent market has a supply and the house has a demand)
Important things to remember with market traders: 1) As with all other access walkers, too many intersections may result in traders not going down a particular road for a long time, resulting in periodic devolution of houses on that road. (2x2 plaza tiles are pretty, but don't build 2x2 intersections). 2) When housing first evolves to a higher level, it can take awhile for the market ladies to supply all of the houses in their area with the higher levels of food/goods demanded/consumed. At first, these houses will have a low supply and therefore the market trader will be delivering large quantities quickly, emptying her parent market quickly, and then she walks around uselessly until the buyer can resupply her market. You may notice that the first several houses she passes get supplied first and evolve while ones passed later get less supplies and take awhile to evolve. There are two things you can do: a) Wait a bit. The houses supplied first won't be given so much on later passes and eventually all houses passed will have a good stockpile of goods and finally the market itself will have a stockpile. Basically, it takes a bit of time to fill up the pipeline from the warehouse/granary to the market to the houses. b) Build more markets. This will accelerate the process if you have plenty of food/goods in your warehouses by creating more market buyers to bring goods from the warehouse/granary to the markets. Eventually, these excess markets can be leveled. I prefer choice (a): if my market traders are going past all of my housing and my granaries/warehouses are within easy walking distance for my market buyers, I know that my housing will evolve and stay stable once the pipeline is filled and the traders have plenty of stuff to deliver when making their rounds.
I believe the main cause of frustration comes from markets being empty due to market buyers having to walk too far for their purchases, resulting in market traders having nothing to deliver (or only some of the commodities needed) to the houses they pass, and from the initial instability of recently evolved houses due to the time it takes for them to build up a stockpile of each type of commodity that they need to maintain their new level. The first is a city design issue entirely under your control. The second is a natural occurance in any market economy (just like the need for signing up on a waiting list at your local EB for the next hot title, to be sure you get a copy before the initial shipment is sold out). You simply need to be aware of it and of your options for dealing with it.