Quote Originally Posted by Hamada View Post
It is for both reasons.
I can confirm that it does not prevent getting them in your party via Duty Finder.
Source: I landed in an Expert Dungeon with someone I added to my blacklist forever ago (around the time Weeping City was brand new). Apparently, they were talking to me, but I couldn’t see what they were saying (I still don’t know what they were saying, and if it was good, bad, or if they even remembered who I was). I only recognized their name because there are very few people on my blacklist, so the ones that are stand out.

Blacklisting does prevent the players from joining PFs in Party Finder that you create, though. It doesn’t work via random DF matching.