There will always be a margin of error in the life of a person who claims to hear from God and yet they are not invested in the word of God. Without His word invested in you, there will always be gaps in the way you decipher and interpret His voice. In the absence of the word even your discernment and insight are compromised. Keep in mind, discernment does not come about through superstition, discernment happens at the instance of your spiritual stability through the word.
You are grounded through the character of scripture and on the basis of that stability you can decipher what is of God and what is not. It's dangerous for a person to audibly speak to base on what they think God is saying. There are many people who went to a place of prayer and returned with speakings that were not of God simply because the basis of their interpretation was based on emotion and intellect.