I agree that economy don\'t need to be as complex as real life economy. Just watch for this:
1. Supply and demand are the base of an economical system.
2. To be effective, an economical system must be almost closed.
3. The circulation of items and money is the key to a good economy.
4. In our world, nothing is created, nothing is lost, all is transformed. It\'s not the case of MMORPGs.
5. In our world, people are tied to their country, state, city and much more. It\'s not the case of MMORPGs\' players.
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First, supply and demand. This is the real base of economy. Get rid of all the government and social stuff and think about it.
A cavern\'s man, let\'s name him Grohk, have 4 wifes and each one have a little garden and makes pots to store food. Grohk\'s neighboor, let\'s name him Bukop, don\'t have a family, but is a young and talented hunter, very good at crafting. Grohk don\'t have silex to produce fire, but he knows winter is coming. He goes to ask Bukop to trade one silex for 10 pots of food and a wife. Bukop want two wifes for it, but Grohk don\'t want to lose two wifes (maybe too much babies to take care of

) He thinks he will be ok if his wifes stay close to him to warm him.
So the winter arrives, a tough one, very cold. The animals are rare and it\'s hard to hunt \'cause of the snow. Getting cold, Grohk travel to Bukop\'s territory with two of his wifes and offer them to Bukop. The neighboor refuse the women and ask for food instead. Grohk offers 10 pots of food, but no girl, and Bukop accepts...
You see, that\'s how it worked. It\'s a fairly simple exemple, but we need to focus on that. The setting of a MMORPG is different from our actual world. The only thing that we can be sure of is that the supply and demand have many chances to lead to market. If there is a King, he will demand for taxes to be paid to the resident. But this is addition to the base system. Can we create a world where supply and demand can be \"realistic\"? Yes. We need to limit supply and create demand.
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Second, the effectivity of a closed circle. To avoid inflation, you need to keep your circle as closed as possible. If you don\'t you\'ll get a nice spiral that we could name continual inflation. To keep you circle closed, you need to control what goes in and what goes out the circle. The inner part of the circle is the \"game coffers\", and the outter part is the \"players coffers\". We need the players to take from \"game coffers\" about the same amount that the players will put back in the \"game coffers\". We don\'t speak of money, but value. When a player buy a sword, he puts money in \"game coffers\" and retreive a sword from them. When he will be selling it, he will add a worn sword to the \"game coffers\" and take some gold from them. It\'s really simple to do when there is no valuables coming from outside the system. These two last points are discussed later, but I think the idea of the closed circle is clear, so I will move on.
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As said before, the circulation of goods between player and system is very important. The majority of players will try to buy the minimum stuff to survive and keep their money to buy the best stuff available in the game. Those people don\'t really participate in the economy because they buy only what they REALLY need (armour, weapon, potions if they, or one of their friend, don\'t have equivalent spells) We need to create needs.
Food is obvious, as is the limited durability of items. Food is not a big issue, because most players, or so, learn to feed themself with what they find around. We could tweak a little to add some depht, like processed food (with \"in town\" equipment) is much more nutritive, and food don\'t keep fresh very long, unless processed. This encourage the players to buy food in town, because they don\'t want to buy the equipment to process the food and want to keep food fresh all their journey long.
The durability must encourage the player to consume products. A worn sword can be repaired for some time, but after a while it becomes cheaper to reforge the sword entirely. Your clothes are not indestructible too, they will get holes in and worn out with time. This is even more true for adventurers. If they buy a nice tricorn with a beautiful white feather on it, I doubt that the feather will survive the fireballs
Services is another way to produce needs. Hiring guards, sellers, searchers, miners, farmers, etc... Transports, housing, banking.
If we can ride horses, maybe they will die in a battle or go away because you don\'t take care of it (and a horse certainly cost a lot)
All those little things can guarantee the players to look for money and exchange it for goods.
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The big problem with MMORPG is that there is always unlimited supplies. In fact, it\'s not true in all MMORPG. Some of them have a limited supply of iron in a region, and a forge can create only a limited number of weapons a day, if they have the right amount of ressources. A project named \"The Dawn\" had in mind to create a real world where all depend on something. The trees cut in a forest will grew back again, but not if you cut the forest itself. Same thing if you kill animals, or all males or female of a species. I think it was a pretty interesting idea, but the project has been postponed. Nevertheless, I think we can use the idea to limit the ressources, simplifying the rules.
We should also have mobs with logical drops. How a rat can drops a full plate? Even if it\'s a giant rat, sounds a little weird. This comes from the D&D system in which the monsters got treasures in their dens or, to the limit, in their stomach (a dragon can eat a lot, but have a stomach for, so it desolves what is in, but you could find magical objects). If orcs spawn in a region, dropping a sword half the time, people will not forge sword, but will kill orcs. We need to give a really special attention to the drops, as they can easily destroy the economical system we created. Keeping a low drop rate and a low drop value will certainly helps. This doesn\'t mean it must not have high value drops, only that these drops must be very rare and related to its previous owner.
Keeping an eye on ressource will permit the system to keep the circle closed. As example: A dwarf gets some iron from a mine and craft it in a sword. The sword is then sold to a human that fight with it a while, visiting the dwarf for repairing it a few times. Each time, the dwarf used a little amount of iron to repair the sword. One fine day the human decided to sell the sword back to the dwarf. The dwarf could repair the sword another time and sell it as it, but he decides to reuse the metal of the sword to make another a new one, but, to do so, he needs some more iron to get a fresh new blade.
In this example, we see the life cycle of the sword. I has been forged, then repaired, then reused. Each step took iron, but it has been spent only on one sword. Except the first amount of iron, each extra can be sent back to the \"world reserve\" of iron. I know, it\'s not realistic, but the system offer interesting possibility anyway.
When people will have forged enough weapons (or any tools) too use all the iron available, they will still need iron to repair or create new things. They will need to reuse their old swords to make new one, as those swords are the only iron left. This should not happen, but it could, if nobody sell/destroy their weapons, but I don\'t think each character needs 10 swords.
If a real and unwanted lack of iron appears (the number of players is much more that what the devs tought) they only have to add some iron to the \"world reserve\" to correct the problem. It could be part of a big event, or the discovery of some new spots rich in iron, or the discovery of a new metal, more resistant. It opens a great number a doors and brings the game to life.
I am sure a similar system can be applied to all other ressources used in PS.
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Finally (that soon?!?

), we can\'t force characters to pay taxes because they are not tied to any specific place, and then have no duty to any lord, king, etc... That\'s true, but characters will want to buy a house, build a guild, open a shop or bazaar. This will tie them to a specific place and if they don\'t pay some taxes to the ruler of the city, they will be evicted. Maybe using a bridge, getting into a town or specific building in a region will cost something. There is a lot of way for a ruler to get some incomes. Paying or not can really influence NPCs reaction. If you never give a tith to the Church and ask for healing, they will charge you a lot more than someone who pay it. They can even refuse to help you. Guards of a city can keep you out. If you give a lot of cash to the ruler, he could have favors toward you and, in a bad situation like being flagged as a criminal, helps you to get out of troubles. This leads to all sort of interesting situations. Maybe you could even secretly pay guards to get into an area prohibited to you (maybe you were banned or it is an area only for nobles, etc..)
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To conclude, I would say that it\'s not the economical rules that are hard to establish, but all what comes with them. Generating good algorythms for supply and demand is just complex enough, IMHO. I would have written much more (even if it\'s longer than I expected) on the subject, but it is going late, so I will let the first impressions on the subject appears before adding anything.
I hope I didn\'t waste my time writting this. Maybe you don\'t agree with me on some points, but I am sure some others are pretty good (cross fingers

)