Random appearance?[]
It doesn't seem to matter for which city you complete the special job. But could it be that he's the first merchant to appear?
Items not for sale?[]
On the desk at the front of the stall was a Daedric Bow Of Damnation, however he was not offering it for sale from his inventory. I sucessfully stole it, but why didn't I have the option to buy it? I'm level 67.
Appearance and Items[]
He appeared first for me as well, coincidence maybe, but dialogue is vague enough in the quest to allow for it to be any vendor for any of the special jobs completed so I cannot be sure.
The Deadric Bow of Damnation you saw, and any other items on display, are a part of Syndus' shop display. All shop displays are seperate from the inventory on the merchant (though they are indicative of what the merchant sells and may, coincidently, be the same item).