[dfinlay]

Another thing to bear in mind is that "Roll your Influence skill to convince person of anything" is somewhat unfair to the Face's player in the same way as "Roll your combat skill to win a fight" is to the Fighter's. That is to say, that if you have allowed someone to play a Face (as opposed to someone who merely has some social skills), you have implicitly promised that Face actions will be an interesting and fun subsystem to engage with in your campaign (or at least that you'll try). That means that important social actions (such as convincing someone to not behead you) shouldn't just be a success/fail roll. Instead, they should be a series of actions, some of which are roleplayed with the support of rolls and some of which are merely tactically planned wherein the face learns what they can about the target and what approach will work for them and then executes it, possibly with some blunders along the way. While you can say (and have a legitimate argument) that figuring out what approach to take and then taking it should be part of the Fast-Talk skill, so a single roll should cover it all, that just isn't fun in the same way that saying "Broadsword (possibly with Tactics) covers what maneuvers to use and how to do them, so roll Broadsword-3 to win the fight" is much fun.

Of course, none of this applies to a lower stakes Face action such as convincing someone to buy you a drink and a QC is perfectly fine here, just as a QC is perfectly fine for a low-stakes sparring match.

That said, you need to actually know stuff about the opposition (their personality, desires, weaknesses, fears, etc) for this to work well.