I don't know if this has been asked before, perhaps with different terminology.
There is a well-known fallacy, that in the realm of religious debates, comes up often especially with regards to "The One True Way of [insert religion]"™, and that is the No True Scotsman Fallacy, which was explained simply thus:
Person A: "No Scotsman puts sugar on his porridge."
Person B: "But my uncle Angus is a Scotsman and he puts sugar on his porridge."
Person A: "But no true Scotsman puts sugar on his porridge." (from Wikipedia)
In other words, appealing to a higher or greater truth is not a way to dispute other views that rise from within the same group being discussed or debated, because what right do you have to claim the truth for yourself? (I hope I defined it properly).
With regards to Judaism, there are several different sects and denominations, and within these there are sub-groups as well, all with differing views on halacha, kabbalah, interpreting the Torah, hashkafah, and so forth. It's not uncommon that when speaking to a non-Jewish party about your Jewish beliefs that they'll ask: "Well, so and so, who's from a different Jewish group, believes X, while you believe Y. How do you know that you're right and he's wrong?" In such a case, answering: "So and so doesn't believe in True Judaism™" doesn't work, because who are you to say what "True Judaism" is?
Therefore, I was wondering whether within Orthodoxy there is a way around this fallacy, or should we simply say: Have emunah, wait for the Mashiach (or work to bring him) and in the end the world will know the truth? True, in some cases it's possible to simply point out internal contradictions within other groups, but the same case can be made against Orthodoxy, as well as considering that this doesn't work 100% of the time.