You are asking for the holy grail of information quality. If such a thing existed, you could eventually eliminate all misinformation. In actuality however, the

You are asking for the holy grail of information quality. If such a thing existed, you could eventually eliminate all misinformation. In actuality however, the contrary happens: people develop bias and prejudice (aka "heuristics") based on incomplete or already misinformed provisional knowledge, which only steers them further away from the truth. Of course there are fairly universal or simply just sound criteria by which you can judge the quality of someone's opinion, but they are not some gold standard and likely most people are already using them. I would say you can even distinguish multiple tiers here, with the higher tiers not being used by less intelligent people. For the lowest tier, take for example good spelling: It can be a weak indicator of someone's intelligence, but then again people might not even speak the language natively, or they were typing on a phone, or they were attending a conference call while reading a paper on matrix factorization at the same time. The same way you could say that quoting reputable sources is only a matter of making the effort and attributing more attention to it. All the while someone who bases their opinion on very weak and unsound arguments might put a whole lot more effort and attention into supporting and solidifying it with such superficial means as spelling or citations. In the end having it or not having it really tells you not much of anything, other than that the author is not totally stupid. Of course we can judge opinions a whole lot better than that, but this literally involves all that we have got and it just can't be pressed into some easy universal ruleset that would work in another person's mind. Something I personally do watch out for a lot is fringe opinion and also someone's attitude speaking to you. You see, someone who is speaking to you on equal footing and who is mostly replicating and reiterating on what most people are already favoring to believe is not very likely to be exceptionally smart and hence unlikely to say anything of substantial value that has not already been said many times over elsewhere (be that for good or bad reasons). People who are really smart have a certain disturbed attitude when communicating about things that are not trivial to us, that stems from the fact that they can't build reciprocal relationships to people who are vastly inferior to them. On the other hand, precisely for that reason very intelligent people can voice opinions that are extremely purposefully engineered to change people's behavior and not to speak out open and honestly on a subject matter. This does of course not apply to fringe opinions that average people discard anyway, which is why I pointed this out. Motive and honesty are very important to consider, but VERY tricky to interpret and most often and easily interpreted wrong or even more often wrong than well by less intelligent people. In the end nothing really saves you from your own stupidity and educating yourself with all the details on the subject.