It may be the work of man, but either God told the authors of the books of the Bible everything that happened, and sometimes even a mix. Moses was even involved in just about everything that happened in exodus. And some of it he didn't even remember because hat happened when he was a baby, so God possibly (though the Bible does not specifically say how Moses found out,) told him everything. Everything he wrote into the book of Genesis came directly from God's mouth. Levi was able to write the book of Matthew because he listened to Jesus' teachings and a little bit because of things he was involved in himself. And the Bible even says that God is always honest and all-knowing. It is the ultimate instruction manual. Whether we are in doubt, need a reference, or are simply curious, we can always believe what we read in God's love note.
The Bible can be trusted. Period. There are dozens of outside sources the confirm the trustworthiness of the Bible including the Pilate stone, the Ammonite Coffin, and the Hittite Tablet. There are scrolls that show its consistency through time such as the Dead Sea Scrolls, and it has zero contradictions; I challenge you to find me ten that cannot be shown to be misunderstanding of text or have another simple answer.
The Bible is open to interpretation. Although it is the foundation for what is known as Christianity, its contents, again depending on interpretation, seem to parallel books or information from other religions, for which there are also historical references. So based on that one could argue the Bible is a reliable source of information.
Of course The Bible can be trusted, it is the inspired word of God. For believers, there is no higher authority, and no greater source. The Bible can be trusted because God can be and should be trusted above all else. For any question or problem we have, we only have to consult Holy Scripture, and we'll find an answer.
Do insects have four legs? Is the sky totally solid? Are the stars smaller than earth? Are bats actually birds, not mammals? Does breeding animals in front of certain branches give certain color patterns? Did an unrecorded worldwide flood happen four thousand years ago? Can two organisms propagate an entire species? No. The Bible can't be trusted. It's factually incorrect. Do you want to stone people who eat shellfish and mix fabrics? I would hope not. It contains quite dumb laws. DO NOT TRUST THIS BOOK.
The Bible is like an epic story that is placed in certain geographical locations and has references to people that can be verified, but the plot of the story cannot be trusted or considered to be non-fiction. The entire basis for trusting the Bible is that it is professed to be written under the inspiration of a being whose very existence is under question.
The Bible cannot be trusted 100% because it is a book written by human men, and men have proven time and time again that they cannot be trusted, especially when put in a position of power. Most people have already learned that religion was used historically as a tool to keep people in line.