I found such an NPC. There is information about him that he is trader on the black market, but I can't buy anything from him or sell too. Is he part of the quest? what does he actually do?
Squeekquek is classified as a Merchant and not your normal Shopkeeper NPC that buys and sells items.
While some Merchant NPCs do buy and sell things, these tend to be of a specialized nature or situation. The Merchants that dont sell anything tend to be there for background/history or as CIPSOFT likes to call it, 'flavour'.
From the dialogue linked here we can see Squeekquek gives some background or 'flavour' about the dungeon called the Corym Black Market and the reason it has so many different and varied creatures
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