I don't like just pure roleplaying to determine trust. I know, I know, damnit. I just don't ok?
It feels a little too much like GM fiat.
"You were captured, your lives hang on your next few words, now dance little man, dance, convince the Gm to let your characters live!"
Is it fun? As someone who GMs all the time, I have to say yes. But I don't think its good game design either.
I also hate with a passion its hard to express the notion that you roll a d20, add a bonus, and live or die.
That d20 roll being a skill check somehow seeming way dumber than a save vs death.
So I'm thinking of using a trust meter. How well you get along with a faction being determined by how thoroughly you've screwed them over in the past.
I like this for a couple reasons. First, it rewards the genuinely nice players out there for being nice. Second, it allows the devious to bide their time, setting up a betrayal that the NPC will never see coming.
Think Arminius leading Varro into the Black Forest.