You missed the points of everything I said.
Let's slow down a little, I just haven't responded to the scripting viability part of it yet. We're talking design theory here, not game limitations just yet.
You said this:
When you think about it, PC merchants do exactly what you suggests.
I responded with this:
This is not how PC merchants operate, and they certainly do not set up shop in the forgotten parts of the world waiting hours to surprise whoever comes by.
This is what I want to get across mainly. They operate in different spheres entirely. One stays in hubs primarily, the other is found out in the world at unexpected places & times. One has a massive inventory, the other has just 2 or 3 choice items.
The closest we can achieve is to design an NPC with a defined merchant store inventory, and have that NPC show up randomly for a spell in certain locations. That is reasonably possible. But like everything we add to the module. it has to have a purpose and have a good reason to be there. To me that means it must offer something others cannot offer.
I personally don't think they need unique items or really good prices to be attractive and worthwhile. Just finding one could be a big break if you can justify shelling out.
It's a shame that the game limitations get in the way.
In this case, the alternative I'd propose would be along the lines of what you said, having a bunch of different merchants with cloned settings, giving each one a bunch of different locations to spawn into, but each one has their own items Merchant A has items ABC, Merchant B has items 123, and so on. It's moderately "exploitable" in that you know each merchant will always have the same items. But that's not necessarily an OOC detail. Each merchant has his specialty, they just don't come around very often.
So even if people catalogue all of it in google docs and spread that info around, there's actually finding them consistently. If the system can't be manipulated by player input, and one only spawns every few days to a week, I feel it just wouldn't be harmful even if the mystique is totally lost on some.
After a full year of every weekly merchant being found and having their entire stock (3 items) bought up -- which is a very generous guess, since people don't walk around with 150K at all times, not even split among their group, right? -- 152 items have entered the hands of players, as opposed to the
thousands that players loot and sell to each other yearly.
Not all of those items are forever - some will be healing belts, quintessences, disease/poison cures, etc. that get used up. Some will be items that grant feats or metamagic, or lower spell slot items, which not all characters keep forever, and an excess of them is not harmful but you might really need one and not want to hit the dungeons that drop them even semi-reliably like 4 times. Some could be Disguise items. These merchants could even sell rare crafting reagents normally only found in loot or something to that effect.
I'm going to assume also that each individual NPC's chance of spawning can be modified somehow, and of these NPCs, only a few out of the dozens in the rotation need to carry anything quite like a resistance belt, or an eye of Ra, greater Geb/Mask. Those merchants in particular could have their prices tuned up a bit more, while the other more common stuff doesn't need to be any more or less affordable than it is when found on regular vendors.
It does also function as a gold sink, since many dungeons are completed without spending any gold, but to acquire these items you must pay. Some money does end up leaving the server forever as a result.
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Just to be clear, I would be totally willing to generate identities (names/descriptions/dialogue) and even learn how to set up a few of these merchants, but I'd rather be certain that this suggestion is not rejected first.