I can't see the objection to iceltic's question. Even if the gospel accounts were written by the people claimed, and I understand there is some doubt about this, it is simply their testimony. Testimony is only as good as the credibility of the witness. For the New Testament:
1 can we even be sure who wrote the testimony and when?
2 could the writers have any motives for lying?
3 could they be mistaken? - some of the testimony is itself hearsay
4 the Jesus character didn't seem to have any objections to proving himself to genuine sceptics eg Thomas. Why would he now?
The answers given so far to iceltic look like evasions to me.
I do not see how anyone can put such faith in a document about which there seems to much uncertainty. Whilst a person is free to believe what they want, convincing others is a different thing. As far as the bible's testimony about itself is concerned: "we'll they would say that wouldn't they?". It's like accepting a tobacco company's marketing about its own product as the undiluted truth.
Before using the bible as proof of God, one must first establish that the Bible is what it claims to be.