ok, I'll send you a PN with screenshots then, but please count on it before 16:00 today...

Update: I have just sent a PN with links to the pictures.
Chanur, I've seen your PM and I reply to it here, in case someone else has some knowledge to offer...
I wonder if I have... ehm... outsmarted myself :facepalm:
You see, I have learnt about the danger in filter dialog for an existing npc, as any other dialog changes involving the same npc might override my changes.
So, I figured out that instead, I would filter the dialog for, in this case, merchant bookseller, male, redguard, location First Edition.
Well... that should work... but... what would happen if the redguard merchant bookseller suddenly isn't a redguard anymore?!
I'm looking at your screenshot, and the guy on it has a beard. My first suspicion is that you are using a mod that changes *some* of the male npcs and give them beards. And that the mods that give them beards will turn them into unique races... like "beardredguard" instead of redguard.
That would for sure explain why you are having problems!
Can anyone confirm this? Or can you give me the name of the beard-mod, Chanur, so that I can look?
Solutions... well, let's first see if my suspicion is right. Then it's a matter of how much knowledge you have with the CS. You could fairly easily re-filter the dialog, or turn the bookseller back to being a normal redguard. or, if you don't know how to do any of this, I can change the dialog filter for you.
But, first we need to know if my suspiscion is right - and I'm so GLAD that you sent that screenie, else I wouldn't had had a clue about how changed the bookseller was in your game.