payn
He'll flip ya...Flip ya for real...
Traditionally, I'd set the table. Who knows the king better or has the upper hand to start? Find the modifiers, roll the skills and check to see who beats who. Proceed from there.So what would be a good system to deal with something like a PC and and NPC having opposed goals and they both go to the king (also an NPC) looking to get the king on their side? The GM can't really argue with himself, so leaving it as a purely roleplaying thing won't work 9unless you enlist another player to temporarily fill one of the NPC roles).
In the case the PC loses, they are going to have to find another solution. That or find more evidence or something that can shift the result in their favor. There is no lets keep talking and roll again in that moment. I might, run it as a skill challenge and the entire party gets a chance to make their case and impact the king, but that's usually like 1-3X a campaign kind of thing.