It seems to be one of two ways - either they profess it to be the absolute truth and haven't actually read it (especially the ancient testament), or they have read the whole thing and concede that it's irreconcilable with their own beliefs, and therefore must have been rewritten and misinterpreted along the way.
This makes arguing about the Bible extremely frustrating, since the only people who'll stand for it are those who don't actually know it.
Which doesn't mean I don't still argue. Maybe it'll actually make some of them read it eventually.
I don't actually have a problem with believers - I do, however, have one with people who'll blindly follow a set of rules without even questioning them, and worse, who actually take offense and become hostile when anyone else questions them.