I imagine there will be some explanation for Faustus' sudden turn. The Red Skull being the Red Skull it's possible Faustus just betrayed him before the Red Skull could do it to him.
My thoughts exactly. Looking back, a turning point would have been Faustus seeing the Skull *not* vowing vengeance when BuckCap shot Sin and Crossbones. Like Azula said in Avatar, Faustus is a people person, and it wouldn't be too hard to reason out that if the man's child and most loyal henchman being shot had no resonance with the Skull, then Faustus' own value might end rather abruptly as well.