"Item hunter" is a sidequest that gets started either by finding one of the 3 artifacts that this sidequests revolves around, or by talking to Lupel in Savina.
If you first talk to Lupel he will tell you that he will buy any rare artifact that you find. If you first find one the items there is simply a journal entry saying "There must be someone who would pay money for this artifact I found." There are 3 items in the game that this sidequest refers to.
The Orb of Glenmorach
The orb is found in Blackwhisper Cave and is simply called 'Strange orb'. When giving it to Lupel he recognizes it as the Orb of Glenmorach and will pay you 30 Pix for it.
This unidentified item is found on the second floor of Grace's itemshop in Bavelock. Lupel does not recognize it but sees it is a very old device. You are given 35 Pix for bringing him the item.
The Shield of Belaphinor
The Shield of Belaphinor is found in the Thieves' Passage. Picking it up you only know it as 'Broken shield'. Lupel recognizes it as an important artifact and pays you 40 Pix for bringing it to him.