If you go to a tribe in Africa, that believe that they are the only ones out there, you won't convince them they aren't, unless they see for themselves..
I never said opinions are plausible, because someone can say, "I think the sky is orange" and it's an opinion.. Are they wrong yes.. Maybe they're color blind? So to them, no one will convince them that the sky isn't orange because that's how they see it...
And yeah, what you said, is a fact.. Because the way you stated it.. A fact Is something that CAN be proven to correspond to experience. So if another person says, "the sky IS orange" then that is a fact because it is something that can be proven.. Even if they are completely wrong..
So in your case. Yes, you saying you are never wrong is a fact.. As for credibility. It can be proven wrong..