No skill-based advice, but I attempted some character assassination in our game. Yuan-Ti had infiltrated the city and were corrupting it from within. The characters had clued in and were starting to stick their nose in the YT's business, and so were offered great sums of cash and land to go off and fight the goblinoids that had massed for war on the mountainous border by one of the imperial representatives, who had fallen under the YT's influence. That failed (they became wary of his offer-why are all the adventurers leaving when there is a threat here?) so YT purebloods dressed up as city guardsmen and jumped the party in a crowded square, proclaiming them agents of evil and that they were under arrest. They realized what was happening immediatly, but were still stuck. They couldn't kill these "guards", that would just prove their assertion true. Running away, ditto. They couldn't go with them, that's a death sentence. The fake guards even called to summon legitimate guards to help them out.
The party was *furious* at me. They were wrongfully accused of being villains and had no clear out. They managed to subdue the fake guards before the real ones showed up while the druid (who had the highest Diplomacy rating) rallied the crowd behind the party with fantastic rolls so they wouldn't jump in. When the real guards arrived, the fakes were knocked out or restrained and the whole situation exposed. They found that to be one of the best encounters in a long time.