I'm posting at work so I'll have to verify names when I get home, but I think I know what is happening here.
I've been quadding Butcherblock dorfs from 41-47 over the last week or so, and I have met two fellow dorf hunters (Yardcore and a necro named Attaq) who have had this problem with being unable to sell to Parn. I, on the other hand, have been able to sell to Parn the whole time (Parn now has something like 550+ Bronze Two-Handed Battle Axes for sale).
The key difference is I have only been killing dorfs on KaladimCitizens faction, which in the dock region would be the two standing on the docks and the two in the huts across from Parn. Often times, when I log on, Attaq is camping the two on the docks and the two male fishermen, so I'll take the two in the huts and run out to grab the two standing outside the dock who are also on KaladimCitizens faction. However, the two male fishermen dorfs at the port have subtle differences in their faction:
Balen Kalgunn: There are no faction hits when you kill him
Thar Kelgand: Among others, you take a MerchantsofKaladim faction hit when you kill him.
I only noticed this yesterday because I attempted to quad the fishermen and two of the KaladimCitizens dorfs. But when I got them below 20%, the fishermen ceased following me. Once I killed them and observed the resulting faction hits, I understood why they weren't social with each other. Thar is on MerchantsofKaladim, et al. faction, while Balen has no apparent faction.
So once I saw Sundawg state that Parn is on MerchantsofKaladim faction, it all made sense. I know for a fact that Attaq waxes Thar as part of his grind, and apparently Yardcore has been also. Thus, Parn hates them. I have only killed Thar once, thus explaining why I have been selling to him the whole time.
Whether or not all of these factions are true to how they were on Live, I have absolutely no idea.