I am working on a browser-based text game. I have implemented NPC shops where the players can buy items in exchange for coins.

Currently, the inventory of the NPC shop is shared among all players. For example, if I sell the shop a Sword, any other player can go to the shop and buy that Sword. This also means if I purchase an item before one of my fellow players, it is no longer available for them. Shop stock is randomly regenerated from a database of possible items and quantities periodically.

I see two options: A shared NPC inventory, or private instances of the NPCs inventory.

What considerations should I have, as far as user experience and the virtual economy, when trying to determine which option to go with?

  • 2
    \$\begingroup\$ This is very much up to you; how do you want it to function? You can design your game around either option. \$\endgroup\$
    – user1430
    Jun 25, 2014 at 17:36
  • 1
    \$\begingroup\$ Bah. I was halfway done with an answer going over upsides and potential negatives and how to solve them. \$\endgroup\$ Jun 25, 2014 at 17:37
  • \$\begingroup\$ I didn't view it that way. I am looking for guidance on the user experience and virtual economy side of things. Would a shared inventory have a negative impact on players who are beat to the punch buying an item? Would an instance-based inventory have an adverse affect on the economy by generating too many items? These are things I do not know and are not based on my opinion. Also, AttackingHobo, if there is some way for you to share that information I would appreciate it. \$\endgroup\$
    – Tyler
    Jun 25, 2014 at 18:02
  • \$\begingroup\$ I think it could fall under the good subjective, specifically the last question. \$\endgroup\$
    – House
    Jun 25, 2014 at 18:11
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    \$\begingroup\$ Possible exploit: When an NPC vendor is the sole source of an important resource, a rich player could buy it all up and then sell it for a higher price. Or just keep it to piss people off. \$\endgroup\$
    – Philipp
    Jun 25, 2014 at 18:50

3 Answers 3


Both methods definitely result in large gameplay variations, so it depends what you're looking for. Here are some thoughts, based on common implementations:


  • Basic necessities should be accessible to everyone. If the shops can be bought out by other players, then there should be an alternate means of acquiring the items (such as crafting). Otherwise you end up with a situation where a rich player buys up everything to hinder the progress of new players.
  • You're going to end up with people sitting around shops, waiting for the refresh. They won't have as much fun (arguably) as the people out exploring, and the people exploring are going to return to empty shops.
  • Inflation of the virtual currency as time goes on is inevitable. If the shop pricing isn't player controller, then quickly enough you will stop seeing any items of value getting sold to the shops, because the price paid is too low (unless you price adjust regularly...).


  • Certain items will become commoditized very quickly; you don't have control over how many of a certain item exist in the world, and thus don't have any control over their economic value.
  • Decreases the sense of a "connected" world.
  • Anything sold through shops won't be rare, and thus will be of lesser "status".

Here are some ideas to make things interesting:

  • What if the stores were shared, but the shop keepers had limited money? They would make more money by selling, lose by buying. They wouldn't need to restock either, everything would be supplied to them by players (from monster drops/crafting). It would keep the store inventory more "balanced", and you could keep the economy from blowing up. Plus, going to the store would always be a new experience. You would only find rare items at high-class stores, because they would be the only ones to afford them.
  • Have a fusion. Basic items, like iron swords, sticks, and so on, would be private instances. But the stores would also have shared items; items sold to them by players. You still run into commoditization issues, but circumvent the problem of rich players hogging everything.
  • Tried-and-true: private instances for basic shops, plus an auction house for shared items.

I'd personally love to try a [multiplayer] game where shopkeepers had limited money; it's not something I've seen before, and I think it would create a really unique kind of game and economy.

As a final note, there are plenty of studies on virtual economies, especially for massively popular games such as World of Warcraft, EVE Online, and Second Life. But I think for this question, RuneScape makes for an excellent case study. This Wiki page has some information on the store system, and how it has change over the years, as well as what the implications were.

  • \$\begingroup\$ Wow limited money while "good" doesn't scale well. I used to get super mad playing Skyrim due to having lots of loot, but the shops having no money to buy it with. This would be made double worse if Player A could drain the shop so player B cannot sell anything. \$\endgroup\$ Jun 26, 2014 at 3:41
  • \$\begingroup\$ @SimeonPilgrim Player C would come along, buy something, so that player B would be able to sell something. Of course there are pitfalls to it, doesn't mean it isn't worth exploring. The real risk is that the shop gets filled with junk that no one wants to purchase. \$\endgroup\$
    – Fault
    Jun 26, 2014 at 9:39
  • \$\begingroup\$ understood about player C but then play D before B can.... As per my answer there is short comings with ether limited or unlimited money/items. It's really hard. \$\endgroup\$ Jun 26, 2014 at 10:05
  • \$\begingroup\$ @SimeonPilgrim Agreed. I suppose the only way to find out a working model is to test and iterate. Another option is to do away with standard shops, and have a trading system that lets players themselves start their own stores. Again, hard to predict what would happen. \$\endgroup\$
    – Fault
    Jun 26, 2014 at 11:14
  • \$\begingroup\$ I also like player shops, it has a good element of understand your customers to thrive. But does it meet the needs of players trying to sell loot to get gold to train etc. If the monster drop stuff nobody values, what the point of the drop. Again, I think the "problems being solved" need to be listed, and then the trade offs of the solutions can be judged. \$\endgroup\$ Jun 26, 2014 at 11:21

All the MUDs I played had the shared shop, infinite money model.

In best one the price was a function of supply, thus selling the first 'rabbit foot' got 250 while the tenth might only get 15. The purchase price was a function of supply also. Thus buy the only 'rabbit foot' cost 400. Also the shop had generation/consumption rates for each item.

The "awesome" items where custom items not limited stock, so in effect you provide input beside money.

Now the mud was still affected by dumping of gear, but higher levels tended to get different dropped gear than the lower levels so there was less cross over.

Which ever model you chose, there is a immersion breaking issues with:

  • a shop have infinite money
  • a shop accepting the 100th item
  • a shop selling unlimited items
  • a shop buying stuff no player/npc needs

which means you have to ask what purpose is the shop serving, a in-out supply shop so more "gaming" can happen? or is trading a large part of the game? or just a money sink?

  • \$\begingroup\$ Sorry for the delay, was unable to access this question from another computer. The supply, price, and generation/consumption is something I am familiar with from the old RuneScape system years ago. It seemed to work rather well but they abandoned that for some reason. Good points with the immersion breaking issues and your final point is a great one. I will need to seriously consider what purpose the NPC shop would really serve, as player shops exist already. \$\endgroup\$
    – Tyler
    Jun 27, 2014 at 20:01

I feel the other answers make too many assumptions outside the scope provided. I think that shared has these pro and con considerations.

Furthermore, I think the restocking option should be revisited on the purpose no matter what option is chosen. Restocking, unless for more realistic impact on the game world, doesn't make any sense if there is a delay. I think a reason on why there is a restock should be clarified more in the underlying mechanics.



  • More realistic system that could be attractable to players.
  • Ability to lock the market, where you can buy everything and resell for higher.
  • Ability to prevent others from buying certain items such as a warfare tactic.


  • Players can troll other players by buying everything in the shop until it's restocked.
  • Players could get frustrated in the buying process if they are to slow to purchase before someone else snags the item.
  • Restocking times can conflict with players play times, especially in diverse time zones.



  • Potentially unlimited and exclusive supply could devalue immersion to the player.
  • No one person controlling the entire market.
  • No one person denying you access to items in the shop.


  • Could devalue immersion for those who want more realism in the shop system.
  • Limited ability to lock the entire market and resell for higher.
  • No ability to deny others access to items in the shop


Locking Down The Market

EVE Online is a player driven economy. Buying low and selling high is a trader tactic that is common in the game. Regardless of who you are buying from, NPC or not, the tactic is very attractable to players.

Likewise, buying all items or useful items from a station is considered a warefare trade tactic. This is to prevent your enemies from getting much needed supplies to fight you or escape. Like the previous example, this is a tactic that is very attractable to players regardless if the seller is an NPC or not.

I feel that this being a negative is entirely subjective.

Market Control

Having control of the market may be attractable for players who want to trade. Although it may be bad for the economy, a bad economy may be a good scenario for the game. I know that sounds bad, but trading in most games is widely popular. Simulating trade, both good and bad trade can be good for the gameplay experience.

For example, a game that include both bubbles and when they burst. Surviving a great depression and more could be both rewarding and challenging for traders, while also destroying the economy. The act of destroying and repairing could be fun for players.

More Realistic

Buying out items and restocking can be looked at as being realistic or a sign of realism in the game. Some players really enjoy these types of designs. Restocking for one good example could include a trade merchant that physically arrives at the shop and restocks it. This opens up additional gameplay experiences for players who may want to hijack the shipment before it even arrives. Likewise, players who want to protect it.


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