One devotee showed me a youtube video about how Mr.Zakir Naik was saying that because a human being wrote the Purnanas and Itihasas it is not considered very authentic especially in comparison to the direct word of God. The stress was given to the "human being". But what he does not know is that there are two types of human beings.
One type is called nitya-baddha beings who are forced to enjoy or suffer the reactions of their past karma or in other words eternally bonded to the laws of karma and this world. Then there are the second type called nitya-Siddha beings who like God walk, talk and perform activities in this world out of their own free will. Unlike the bonded beings, these eternally liberated beings are not bound to the laws of this world. Mahamuni Vyas is one such liberated entity came to this world specifically for the benefit of mankind and when He writes the Puranas or Itihasas we have to consider it as good as the word of God.
Krishna Himself directly speaks in the Srimad Bhagavatam on the position of such an acharya or liberated being.
ācāryaṁ māṁ vijānīyān
One should know the ācārya as Myself and never disrespect him in any way. One should not envy him, thinking him an ordinary man, for he is the representative of all the demigods. - SB 11.17.27
So yes they may appear as human beings but they are not like ordinary human beings who are attracted to the razzle and dazzle of this world reaping their own karma. They are supremely independent in the full shelter of God or Krishna. We need to be aware of this distinction.