And how would you actually go about proving Roose's guilt in this case?
Player: "King Robb, Young Wolf, I bear news of a terrible development in the Bolton lands! Lord Roose Bolton is plotting with Tywin Lannister AND Walder Frey against you!"
* Persuasion attempt successful!
Robb: "Ack! It is hard to believe, but you've managed to convince me to listen to your words. Men! Declare the Boltons traitors of the realm and sent out a hunting party after the head of The Leech Lord himself! Now, my loyal [CHARACTER NAME], what evidence can you present in case we must take this into court for trial?"
Player: "Uhhh.... uhhhh.... I've heard others say the same."
Robb: "..."
Player: "I read it in a book, okay?"
Robb:
[are you f*cking kidding me what the f*ck does this guy think he's playing at for f*ck's sakes eddard give me strength not to kill him]
* Relations with Robb "are you f*cking kidding me" Stark dropped by 200!
Player: "Mudcrabs, ugh. Disgusting creatures."
Seriously, plot probability: everyone's suspension of disbelief would fly out of the window if you could convince ANYONE to execute another lord through a simple relation/persuasion check without evidence, or even with a small amount of more or less significant evidence. It just don't work this way in life, son.