if you are deeply rooted in your believes and/or religion- it will be easier to detect false prophets. you know and understand what you beleive in and will question anything else that might say otherwise.
if you're not- well, you'll be easily swayed.
Do we still need prophets and for what reason?
A Great Prophet must be a great man to begin with. He must be an upstanding human being with a benevolent character and must possess great wisdom in order to qualify for God's counsel and grace.
He must also have a long white beard similar to the guy's beard in this picture.
A long white beard is required.