The Prophecy Argument
(fulfilled prophecy):

Some people tend to use fulfilled prophecy as an argument for the existence of God and sometimes also for the omnipotence and reliability of God.
Prophecy is a prediction of future events and fulfilment is the reality of those future events that appear according to the prophecy.

False Prophecy verses
The bible says a prophet who speaks false prophecy in God’s name should be put to death, that if a prophecy does not come true then it was not a prophecy from God and that true prophecies can come from things besides God (Deuteronomy 13:1-5 and Deuteronomy 18:20-22).

Conditional Warnings
However, not all prophecies in the bible are unchanging predictions but sometimes conditional warnings about what could or would happen if people’s behavior were a certain way or didn’t change (Deuteronomy 28:1-2, Deuteronomy 28:15, Jonah 3:7-10).

There are also prophecies in the bible referring to messages from God (not foretelling but forthtelling) intended to strengthen, encourage, comfort and edify people (Romans 12:6, 1 Corinthians 12:7-10 and 1 Corinthians 14:3-4).

Common Prophecy Flaws:

• Retrodictive:
  Tends to be made known, modified or reinterpreted after what appears to be the fulfilment has already happened.

• Unintentional:
  Tends to not state that it is actually intended to be a prediction of future events.

• Vague:
  Tends to be vague, containing ambiguous language with various possible interpretations.

• General:
  Tends to not be specific but general, not having a specific time frame or location within which the events must occur, and contain events that could happen within various circumstances.

• Ordinary:
  Tends to contain normal events that often takes place or events that can probably happen sometime in the future without any supernatural intervention.

• Self-fulfilling:
  Tends to contain events that can happen through mere human intervention. When prophecy is made known to people, the mere fact that people are aware of it can increase the probability of it being fulfilled whether people are aware of how they’re contributing towards it or not.

• Matching reality with expectation: It is assumed in advance that prophecy will be fulfilled without examining the reliability of the source and the clarity, accuracy and specificity of the contents and what appears to be the fulfilment.
  Based on perception of the prophecies, the expectations of the future are shaped and present circumstances are perceived according to the expectations.
  This results in trying to match reality with expectations instead of trying to see reality as it actually is.

A book containing prophecy and later mentioning its fulfilment is not in itself a demonstration of the truth of the prophecy, it's merely claim.
Someone proclaiming a book to contain many prophecies, only some of which appear to have been fulfilled while others remain unfulfilled, is not a reliable source.

Reasons for accuracy
If a book (or person) were able to reliably, clearly, accurately and specifically predict future events, we should consider various possible explanations before drawing any conclusions.
This doesn’t necessarily demonstrate the existence of God; it only demonstrates that there was somehow knowledge available about the future.
Furthermore, this would not necessarily mean that any other things mentioned in the book (or by the person) would also be true.
Each event would have to be examined independently; we should avoid drawing a conclusion based solely on our personal preference.
The explanation could be natural. Unless we are able to rule out naturalistic explanations, concluding that it was God without good evidence is merely an assumption based on our bias.
We currently don’t have good evidence for God being able to reliably, clearly, accurately and specifically predict future events.

Using the scienctific method, we are able to make predictions of future events using the best available evidence we currently have.
This is how we can reasonably predict the future. However, our predictions are fallible. If an omniscient and omnipotent God exists, that God should be able to make infallible predictions of the future all the time and provide us with good evidence and reason that is convincing to rational people. However, this has so far not been the case.

The bible contains various failed prophecies and sometimes claims that certain events were the fulfilment of earlier mentioned prophecies without clearly explaining the connection between the prophecy and what appears to be its fulfilment.