It is easy to learn where a person is coming from. Just listen to what they say and watch what they do.
Read: Luke 6:44-45
44 A tree is identified by its fruit. Figs are never gathered
from thornbushes, and grapes are not picked from bramble bushes.
45 A good person produces good things from the treasury of a
good heart, and an evil person produces evil things from the
treasury of an evil heart. What you say flows from what is
in your heart.