Well I certainly can't pledge that we check everything, but mods who have access to an academic library or otherwise can google will quietly follow-up on the sources on posts that sound iffy. Sources used in flair application posts are also spot-checked. Any source that's completely made up will be spotted very easily. If I (I have a library degree) can't find something from a citation it almost certainly doesn't exist.

Usually however it's patently obvious when someone doesn't know what they're talking about - like when they're pushed for sources they'll copy and paste the ones at the bottom of the Wikipedia article they're working off of and not even edit the formatting. Not being hyperbolic, this happens. And they are duly terminated with extreme prejudice.

Our academic training (or fun hobby) requires we read and synthesize a tremendous volume of information in our specialty. On some topics, particularly the ones within our specific area of interest, we have a really good understanding of the major historians/anthropologists, their ideas, their published works, and the nuances of major debates on the topic. In the wider sense, we have a solid background in our region/time period and can quickly find and check sources, if needed, when a strange question/source arises in threads. Someone trying to fake references, or cite some random person who we know not to be involved in that area of research and debate, would raise red flags and I would automatically question/follow the source.

Also, do you know the phrase "don't BS a BS-er"? Well, that works for many of us. We were all students once, we've all tried the BS, the weasel words, and the half-truths used to conceal ignorance of a topic. We can recognize when someone is talking outside their area of expertise by the way they present evidence, frame a debate, or arrive at their conclusions. For example, someone a while back posted and AMA in /r/IAMA claiming to be a Near Eastern archaeologist. I read through the AMA, and my BS detector kept going off. The answers were written at a mid-level undergrad level, not a professional archaeologist. Lo and behold, a few hours later the guy admitted to faking everything and the thread was taken down. If my BS detector is going off, I will likely check up the sources and see where the OP is getting their information.

Also, do you know the phrase "don't BS a BS-er"? Well, that works for many of us. We were all students once, we've all tried the BS, the weasel words, and the half-truths used to conceal ignorance of a topic. We can recognize when someone is talking outside their area of expertise by the way they present evidence, frame a debate, or arrive at their conclusions.

I have to agree fully with /u/anthropology_nerd with this statement. It's usually incredibly easy to tell when someone is bullshitting. Even if someone puts a bunch of relevant material at the end it's easy to tell when they don't have a lick of sense about them. This comes from both, as said above a refined BS meter, but also just general knowledge about the field.

What is far more likely than someone just making up a source is someone going onto amazon or our book list for instance and just dropping in random book titles to back up their bullshit. For that we have the luxury of a large userbase who have read these works or are expert enough to call out this bullshit when it occurs -- something I have done more than a few times. Usually people who indiscriminately just copy sources don't know which to choose; more than a few times I've seen someone get called out for citing a book published in 1910 or something that has been already disproven or from a non-academic publisher or whatever.

This is why publication data is important. For example,

John Smith. Medieval Europe. (Cambridge University Press, 2013)

John Brown. Medieval Europe. (United Free Press of the East, 2012)

Even if both are legitimate, which one would you trust more just based on who published it? The same goes for journals. Most big journal are published somewhere fancy - the AHR is through Oxford Univ. Press, for example. Smaller ones, like Arthuriana are still usually published through an academic publishing house. If nothing else, google the author or the editor.

More practically, if you can't find it on a database like Worldcat, it probably doesn't exist or isn't worth looking at.

Edit: For area specific questions, I would anticipate most of us with flair wouldn't hesitate long to call the poster out on BS - I've been corrected myself before, too.