[MUD-Dev] Economic Growth: NPC pricing

[Adam Martin]

From: "Timothy Dang" <tdang at U.Arizona.EDU>
> On Tue, 18 Dec 2001, Bobby Martin wrote:

>> My half-formed ideas regarding integrating NPCs into the economy
>> are to have the NPCs know a local market price (by monitoring
>> exchanges on the server) and scarcity.  For some default
>> scarcity, they want to sell at e.g. 110% market price and buy at
>> e.g. 80% of market price.

...

>> If an item begins to be scarce, either in their inventory or in
>> the local area in general, they simply raise their estimate of
>> the market price by 10%.  If they are still selling at those
>> prices, they raise the price still further.  Essentially, my hope
>> is to arrange things so that NPC merchants virtually never sell
>> out of an item unless they decide not to deal in the item any
>> more.  The reason they don't sell out is that the price goes to
>> infinity as their inventory goes to zero.

> I've generally been down on trying to make NPC merchants active
> economic participants, but at first glance I imagine something
> like this could work because of player arbitrage. If NPCs each
> keep separate measures of appropriate price, and adjust their own
> prices independently of each other (which means using the
> individual NPCs state, not the regional state, for information),
> any individual NPC may get some prices out of whack.

> However, if the prices get too out of whack, then you'd expect
> players to arbitrage those prices between the different NPC
> merchants. In order for this to work well, you'd probably need
> each NPC to have unlimited stock and funds, though.

> If done carefully, I don't see any way for players to game such a
> system.  But it's easy to miss those things until its too
> late. One minor detail is that you'd need to program trades with
> the merchant so a player couldn't see that arrows are currently
> 100GP each, and sell 100 arrows at once at that price. Instead,
> the merchant would need to adjust the price-per arrow (or
> presented as total price) for each new arrow offered to be bought
> (or sold).

My knowledge of what current MUD's are doing is scant to say the
least, but I do know that Runescape has been operating this system
most of the time it has been running. Andrew (the author) changed
from "one price suits all" to "exponential price increase the
scarcer the item is in the NPC inventory".

This seems to work well, as the last item of any type tends to hang
around in the shop up until the moment someone is *really* desperate
for it. Note that for "naturally" expensive items, the lowest
possible selling price is commensurately high - I suspect he has the
decay function for increased availability pegged to something like a
minimum of 40% of the price when there is only one item available.

All shops have unlimited supply of about 5-10 items (the basic items
essential for trade skills, or the 2-3 most basic
weapons/armour/shields, dependent on the type of shop), so there are
no chances taken with someone DoS'ing newbies from the basic
activities.

Adam M

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