How can I be sure where a person is coming from, such as a person who seems to be holy, but then changes their ways to negative vibes all the time?
Galatians 6:7
ESV - 7 Do not be deceived: God is not mocked, for whatever one sows, that will he also reap.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Satan will ALWAYS lead you to aid him, putting you outside of the family of God.
God will always cause you to what is good and right for YOU to do, and it will affect you from the GOOD side, not Evil as with Satan.