Big boy tower

[HoboKnight]

Hey guys, I could use some more of your brainstorming with worldbuilding.

I am running a low-magic setting(Faerun, Spellplague, magic items above Uncommon are rare). My group, however, has, through invested time and perseverance, reached level 12. So they were looking for a place to get some more powerful stuff and have travelled to a large city of Iriaebor. After asking around at minor shopkeepers(common potions of healing and funny-yet-not-very-useful-magic-trinkets) they were informed of The Market. It is an unassuming tower in Iriaebor, owned by The Merchant(who is an Archmage) and has a Shield Guardian servant. Entry fee is 10.000 gp.

Here is how it works: By paying 10.000 gp, you get access to the market. Meaning: You just found Ring of Djinni Summoning in some higher-tier dungeon, but deem it kinda useless for your party. You bring the ring to the Market and announce, ti is there for trade. Other Market members are notified of this and when an item is introduced onto market and item is of same rarity, you can exchange it. Gold is meaningless at this point.
Another option is location - clearing. There are a number of locations that are still unlooted. After paying a fee, you can go try crack this loaction and possibly get something to trade in for an item you want.

My party got a "location" quest and is doing really good. As they return, it will be known they took down a number of vampires and two adult dragons, so... i think powers that be should notice them.

Who/what should these powers be? I was thinking other Market members like higher-level adventuring groups and perhaps an arch-lich magic item collector, as well as a couple of archmages who trade on the Market.

Since they are travelling a lot, their renown was really low(except one Paladin), so this is the takeoff point for them. Who would knock on their doors, since they are now known as new smiters on the block?

Thnaks :)

[Amnestic]

If they killed two dragons (presumably Evil ones?) then that might get the attention of the opposite type of dragons (presumably Good ones?). Dragons, of course, notable for having a hoard of gold and magic item.

If you wanted a large group to get interested, the Knights of Bahamut from the Minsc+Boo book could be adapted into getting involved too?

Lathander and Kelemvor are two gods that aren't super thrilled about undead being around, so they could have attracted the attention of one of their Churches? They likewise often have decent stocks of relics.

[Corran]

Two competing bards (the closest thing to a journalist I suppose). Each one wants to earn the right to tell their heroics in song or poem. The pc's may have to choose which one does (although one of the bards might be petty and if rejected might do it anyway but not in a desirable fashion; you can never be too careful with your fame...).

Then have their heroics reach as entertainment high social circles, so the pc's may be invited to the courts of some lords or whatever. Opportunity to throw a bit of social roleplay their way. Since it can be fun messing with paladins, I would present them a roleplaying situation where the pc's get praised for acts of goodness they did not commit (eg you are different from all those other supposed heroes who are only after trinkets, you saved the poor children that the vile dragon was threatening to eat, you are trully heroes), because the bard got a little carried away with telling their tale.

And then I'd follow that up with an opportunity for a more selfless quest (eg they are approached by an individual who offers them a quest of freeing a village that's run over by vampires; with their skill, all it would take would be to travel through this magic portal to reach the village -have it be seen from the other side, end the foul beasts and free the survivors who are kept as blood bugs). And of course that quest would be a trap - one of the downsides of gaining a reputation, if you can pull off making such a cliche a surprise (make them feel bad by showing that they could be doing more selfless quests, but most importantly, make the quest giver look forced or desperate to offer them this quest and make him not shy at expressing his doubts over their morality and competence; because there's nothing like unappreciative NPC's to make your players want to prove something).

[Unoriginal]

You could have the Power-that-Be be Acererak.

He set up that "Market" as a way to know where various magic items are and who have them. If there is something he wants he can just shows up and take it after murdering the current owner.

And the "location clearing" requests are a good way to a) destroy the lairs and plans of potential annoyances without lifting a finger b) get to learn the locations of more magic items and secrets c) make sure that any request to clear a location that is important for Acererak's schemes gets subtly stone-walled into irrelevance d) make sure that anyone who discover or wish to clear one of the locations that is important for his schemes is known to him and can be dealt with and e) send adventurers who have something of interest (ranging from "they're from a family Acererak has a grudge against" to "that magic sword they found is notably powerful") to dungeons set up by Acererak to destroy them.

Of course the Archlich isn't going to run that himself, but a Devil or Construct or cursed-enough entity can be made to do the job without deviating from his vision and plans.

[Nagog]

It could be fun for a Devil to offer them power (and Multiclassing capabilities) in exchange for a magic item. If those items are as rare as you say, they're worth more than an unwilling Soul, so no strings attached, just ownership of a powerful magic item.