A very frustrating thing you can see online, or even in books, is the tendency of people to simply copy a quote or claim without verifying the source at all. Thus one ends up with people throwing around false or at least misrepresented quotes all the time. It's especially frustrating because nowadays it's so much easier to check on these things.
Let's take an example. I saw someone say that that Winston Churchill said "The best argument against Democracy is a five-minute conversation with the average voter." They gave no source. But discovering that there seems no evidence he said that should have been easy. All you have to do is take the quote, put it into a search engine, and see what comes up. If you find sources, all well and good. If you just find people repeating it without a source, or find people saying it's not true, then that's an indication it's not a true quote.
In this case, what happens if you put it into a search engine? What turns up for me are a few sites giving the quote with no citation, and some other sites saying there's no evidence at all he ever said it, like this one. It would have been very easy for someone, prior to claiming Winston Churchill said it, do a very quick search and see what turned up. But unfortunately, people don't do that. Granted, someone can say the quote (irrespective of who said it) is accurate, but it's still wrong to attribute it to someone who never said it.
For a contrast, let's consider the quote "The only thing we have to fear is fear itself" by Franklin Roosevelt. If you put that into a search engine, the top results immediately give you sources, saying it's from his inaugural address. Indeed, the text of said address can be seen here and therefore verified. In a case like this, you can be sure the quote is accurate.
So before you go around posting a quote attributed to someone, please do just a quick search online for it to try to verify it's true. If you find evidence it's real, go ahead! But if you just find people saying it without a source--and especially if you find people saying it's not true at all--you should hesitate before accepting it as true and repeating it.
This also applies to "quotes lists" that people sometimes use in arguments. That is, they'll give a big string of quotes from people or from books to make some kind of argument. Many times, these quotes are simply copied from other sources without any attempt at verification. Before you offer one of these sorts of "quotes list", try to verify the quotes.
Of course, sometimes things can be a bit more complicated. Sometimes people do cite a source, but just because a source is cited doesn't mean it's necessarily true or represented properly. If one is trying to use a quote in an argument of some sort, you really should if possible make a point to verify it. One doesn't even necessarily have to get a physical copy; sources like the Internet Archive (my personal favorite), Google Books, Project Gutenberg, and HathiTrust allow you to read a number of sources for free online, though only the first two tend to have anything that's still copyrighted. In some cases you still have to look at the physical book itself, but my point is that many times you can check in the comfort of your own home. And even if you can't, you can go to WorldCat to see if there's any libraries with it, and even if not, various libraries let you make loan requests in which you identify the book you want and they can see if another library will loan it to them temporarily you. In fact, if it's only a few pages you want, you may be able to request those, which will allow them to simply scan those pages and send them to you electronically.
Of course, sometimes people offer a source, but it is cited very confusingly and it's difficult to figure out what the citation even is. In cases like this, usually it means it's just copied from someone else without checking. In such cases, again you should be very cautious in trusting them.
So what is perhaps the takeaway from all of this? Just because you see a quote attributed to someone (or to a work) on the Internet does not mean it's necessarily true. Plenty of times people will constantly be sharing quotes that are false even though it should be easy to check them. Nowadays there is just not an excuse for not doing the minimum amount of work to make sure that a quote is accurate nowadays, especially if you're using the quote in the context of some kind of argument.
So, again, before you repeat a quote you saw someone attribute to a particular person or a particular work, try to verify it. Put a search for it online and see what comes up. If a source is given, try to check it if possible. If you can't find a source or all the sources listed are confusing and hard to figure out, maybe you shouldn't try to assert the quote in question as fact.
Maybe this blog post will have no effect whatsoever, even to those who read this, and is just me screaming out into the wind. But if it makes even just one person more cognizant of the fact they should try to verify things before repeating them, I suppose it will have done its part.