@Rinel I quite loved the paranoia of who is, or might be, a darkfriend - sometimes based on very minor clues, any bit of irregular behavior, that one thing someone said that one time, etc.
It seems a bit more common now that we've seen the same thing a bunch of times in the form of Skrulls, Cylons, etc... but I feel back then it was a brand new, cool concept: Paranoia in fantasy.
This is one of the main reasons I was sad when RJ passed on, because I really wanted to see Cadsuane's potential outrigger novel, especially the part where she found out the Black Ajah was A) real; and B) she avoided being assassinated by them for likely a number of years (although, warding your chambers seemed to be a great way to avoid that and we don't know if Cadsuane ever got on their list of KILL HER). Granted, she had a bit of an advantage thanks to her Power-negating ter'angreal, but that doesn't mean she can simply ignore the Oaths or assume a given individual was a Darkfriend to defend herself in the event of a surprise attack.