The Bible says (Hebrews 11:1) that "faith" is "the substance of things hoped for, the evidence of things not seen." But I don’t think you can tell from that whether anyone has faith or not.

However, there is a better way. Don’t go by what someone says. Watch what he or she does, instead.

Here’s a little story to illustrate the point.

Once upon a time, a man was driving recklessly down a dangerous, narrow, twisting and turning mountain road. All of a sudden, the car spun out of control and went over the edge. The driver temporarily saved himself by reaching out and grabbing hold of a shrub part way down the precipice as the car hurtled towards the bottom of the canyon some 2,000 feet below. Hanging in space with no apparent way of saving himself, the man begins to plead with God.