Incarnate is a pretty heavy term; there's only one that incarnates the truth: Jesus.
As per John's Gospel's first chapter.
As for telling which people to listen to, 1 John 4 tells how.
Evil is incarnate in all of us, every day. The devil can do nothing of his own power. We must give him permission to use us. The “Trickster” lies to us, persuades us that evil is good and good evil. Because our will is weak, damaged by the Fall, and our minds darkened and confused. We have a hard time sorting it all out. But God has given us guides, not only the angels, but the saints as models, and often saints we encounter in passing on the streets. But also demons, and again, we must pray that we be able to discern one from the other.