Oh, they know they are faking it, but it is all justifiable.
No, they don't, it's part of their personality disorder that they are charming and pleasant. They aren't OTT in their charm, they appear often as pleasant sociable people because that's what part of their personality is, that it changes when with a partner they abuse is also part and parcel of their personality. They have a tremendous sense of entitlement and often life they think conspires against them so that any failures are never their fault but they've been dragged down usually by their partner. They will often genuinely decry domestic violence, bullying etc because they don't see that is what they do. They also have an instinct almost about weaknesses in other people which they exploit, this is one reason we need to bring up children to be strong, well rounded people without lack of self esteem and with no self confidence issues. People basically who are happy and confident in themselves and are not fodder for the abusers.