We're open for discussion or the laying out of more positions, but I'm not going to wait for them to discuss the ones we have at hand.
For the practicing (or professing) Christian, what's the standard for what to believe? For those most loyal to a denomination or a church, the answer is usually simple- the official stance of their group is correct no matter what. So, to them, truth is about conformity and/or popularity. That's definitely not my style, but I admit it sure keeps things simple and is very fast, requiring no work on their own behalf.
For some, the answer may be more of "the long-held answers have been tested, so they're most likely correct". That can look just like the previous category, but has a bit more flexibility of idea, that is, that poor ideas may have been rejected. Certainly many of the silliest attempts at doctrine get excluded this way, so it's not without merit (although it's not my style, either.)
Around this messageboard, it's no shock to see "sola scriptura" discussed or respected- that is, what's correct is what the Bible says, and mistakes are from either not reading it, or no understanding it, or not even trying to use it for a basis of doctrine or beliefs. Like all systems, this one isn't perfect, either. If your translation is faulty, your understanding will be faulty. If you don't understand your terms, your understanding will be faulty. If you come with preconceived notions, your understanding will be faulty. (Naturally, if the entire position is wrong, the same will result, but I count that under the translation being faulty.)
That having been said, plenty of people who sincerely claimed they agreed with the Bible have disagreed with each other's positions, so it should come as no shock that those aforementioned problems are nothing small.