A false prophet isn't someone who gets a word wrong, it is someone who has an evil heart.  Matthew 7 reveals a common thread for false prophets which is lawlessness in that they hear the word of God, but do not do it. 

1 John 4 reveals a test for a false prophet.  They don't acknowledge the redemptive power of God; they don't listen; nor do they love.  False prophets use fear and fear of punishment as a main motivation in their ministry to get people to do what they predict.