How did people know that their visions of God were not false before the Bible was as a book compiled?

I looked at many Christian apologist websites, like GotQuestions, which states that anybody who claims to see God can have their claims evaluated by Scripture. So far so good, but how would people like Abraham know that their visions of God were real and that they were not deceived if they didn't have the complete edition of the Scripture?

The existence of God is not dependent upon the existence of the scriptures. The scriptures simply tell us what God did or said in the past and details specific interactions with certain people or groups of people.

God's interactions with Adam and Eve, Noah, Abraham were written down after the events took place. When God told Adam and Eve there would be consequences for eating the fruit, did they experience the consequences? When God told Noah there would be a flood, was there a flood? When God made a promise that his old wife would have a son, did she have a son? The supernatural events that spoke to the validity of God's words miraculously came to pass.

In the same way: Peter, James, John, Matthew, Luke, Mark, Paul, and the other followers of Jesus didn't put their faith in Jesus because of the New Testament. They believed who he claimed to be because of what they saw. Then a few year later they recorded what Jesus said and did.

Additionally a person today can look at the evidence of their own sinfulness, hear a quick message that God created them, their sin separates them from God, and the God sent His Son Jesus to die and rise from the dead for their sins and they can place their faith in Him without ever knowing that there is a book that contains God's written history with humanity.

1. The first means is fulfilled prophecy.

   • Methusaleh's name was a prophecy: it means "When he dies, it will come". The year he died, the flood of Noah arrived.
   • God told Abraham that he would have a son. Twenty-five years later, he did.
   • Elihu announced the coming of God to Job, and God came.
   • Job uttered at least two dozen prophecies, which ultimately came true.
   • Joseph had dreams, interpreted them correctly, and the events came to pass.
   • Moses asked God for a sign that he would succeed in rescuing his people from Egypt:

12 And God said, “I will be with you. And this will be the sign to you that it is I who have sent you: When you have brought the people out of Egypt, you will worship God on this mountain.” (Exodus 3:12)

2. The second means is miracles.

   • Enoch did not die, but was taken up into heaven
   • The wombs of all the women in Pharaoh's household were first shut, then opened because of how he treated Abraham
   • The plagues against Egypt certified what God told Moses
   • Job's healing and the restoration of his fortune and long life certified what God told Job

3. The third means is righteous character and loyalty to God in the midst of suffering and persecution:

   • Joseph refused to sleep with his master's wife while a slave.
   • Job was already a righteous man, yet when he suffered, he did not curse God.
   • Lot maintained his character and hospitality though surrounded by a completely wicked culture.
   • Abraham refused to accept the spoils of war from the unrighteous kings he was forced to ally himself with.

4. A consistent message, regardless of the medium of communication emplyed by God. In my study of Job, I counted thirteen different means of communication employed by Job and God to communicate with one another, and the different pieces assembled from all those means fit together harmoniously.

5. Faith in God despite impossible circumstances.

   • Abraham waiting all those years for a son, then being asked to sacrifice him
   • Jacob, enduring years of false dealing by his uncle Laban
   • Joseph in prison, believing God would set him free
   • Job, on the verge of death, believing that God will raise him from the dead
   • Moses before Pharaoh, believing God would set his people free

6. The Holy Spirit. The Spirit grants wisdom and many other gifts. When a life displays that fruit, it is persuasive.