Should an NPC shop provide a unique or shared inventory for each player?

Question

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?

Answer 1

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

Shared

• 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...).

Private

• 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.

Answer 2

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?

Answer 3

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.

Shared

Pros

• 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.

Cons

• 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.

Private

Pros

• 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.

Cons

• 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

Explanations

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.