random npc merchants

[Nihm]

These would have a chance of appearing in the stalls outside on the ziggurat, or the market inside it, or perhaps in one of the taverns.  There might also be one of these in the wilderness similar to the Wandering Duergar merchant.
 
These merchants might sell things for a little cheaper than the standard ones, or might sell things such as maps or keys to rare places or rare alchemy recipes.  In the latter case you wouldn't get to see what it was, it would be a dialogue option to buy it without seeing it.  One of them might even have an errand quest.
 
This would give people more of a reason to cluster together near the market stalls and would relieve the somewhat drab and predictable state of the npc market.

[ExileStrife]

I think the NPC market should be drab and predictable.  The PC market is where the interest and excitement should be.

[Drakill Tannan]

Unfortunetly, the PC market can only be of items dropped or given in quests. And if such is the case, a PC can quest for the items.

I think the idea is to have uncommon or powerfull items only buyable from this occacional and rare merchants.

[Disco]

I like this idea. I really miss that old duergar merchant. He was always fun to look for.

[TheImpossibleDream]

There is already a random npc merchant that sells a variety of really awesome items and even more awesome potions.