Have you ever thought about the fact that many angels were deceived by Satan? They lived with God in Heaven and were cast out along with Lucifer to the Earth.
What about Eve? She walked and talked with God in the cool of the day and yet she was deceived by Satan. Her and Adam were both cast out of the Garden of Eden soon after.
Why is it that we often feel that we could never be deceived by the devil? We have this attitude that we would never fall for any lie or trick the devil told us. Are we giving the devil enough credit? Have we forgotten that the Bible tells us that Satan is the lord of this world and has blinded the minds of the unbelieving? (2 Cor 4:4) And that he masquerades as an angel of light. (2 Cor 11:14) He wants nothing more than for us to feel comfortable and secure in something that is a lie and false. The root of deception is that fact it blinds us to the fact we have been deceived. He does not want us to see the truth that is in God's word. Why? Because he wants our souls and the souls of those around us. How then can we know if we have been deceived or not? The only thing that one can do is seek the truth in the only absolute truth... God's word.
I pray that you will test yourselves, prove yourself to be in the faith! Eternity is too long to miss.