Trusting Historical "Facts"

I haven't decided how particular I am on trusting historical facts. There seem to be so many things that become popular, regardless of how true they are. I just don't know who to believe anymore.

Speaking particularly of Biblical Interpretation, I don't know what resources to trust. There are books which claim that the reference Jesus makes to "a camel going through the eye of the needle" refers to a gate which was called the eye of the needle. There are also references which claim that this is made up, and wasn't even mentioned until 1000 AD or so. Who do you believe?

What about on more vague things. I'm doing an exegesis paper on 1 Corinthians 15 this weekend. As part of the assignment, I have to do a decent amount of historical work of Corinth, and particularly, the church at Corinth. I've heard often of the immorality in Corinthian society that came from being a major trade center because of its port, but the Bible dictionary I was reading today states that it would have passed before Paul evangelized the area. Thus saying, Corinthian history is true when it says it has this past of enormous immorality, but to claim that it was in that state when Paul wrote to them is wrong.

Who do you trust? Can I assume a standard of morality worse than the norm in Corinth when reading the Bible or not? Do I trust the books written in 1980 that say I can more than the ones written in 2002 that say I can't? Do either of them have a better "historical" footing than the other?