Academia has a dark side. Some scholars have published work that turns out not to be reproducible, as a result of data fraud or even complete data fabrication. You can read plenty of stories about such dishonesty on Retraction Watch - some are stories about errors in methodology, and researchers jumping too quickly to conclusions, whereas other retraction are the result of fraud.
By now, the dark side is present at all levels. Undergraduate students can buy their essays (and typing this sentence makes my stomach churn, as I'm sure this post will be flooded with spam comments from paper mills). Graduate students can buy their thesis online. And some professors who may feel pressed for extra income contribute as ghost writers to this system. The for-profit cycle of academia is complete (and has sent some students and academics completely out of orbit).
In an extreme case, a dean who exposed academic fraud in South Africa was murdered. One of the men accused for murder is a former colleague of the murdered dean. When people have a lot to lose, they can become extremely desperate.
Paper mills are websites that churn out on-demand essays for students at all levels. And the use of paper mills is on the rise. According to this article from the Times Higher Education "one large essay-writing company says that it has seen a 20 per cent increase in the number of UK customers in the past two years."
Ellis, Zucker, and Randall (2018) studied this problem and managed to find the cracks in the system of paper mills to learn more about their business model. Their analysis show that the paper mills are a mature business, and they offer some recommendations for academics to detect fraud.
If you want an intriguing look into the life on the other side of the paper mill, read "The Shadow Scholar: How I Made a Living Helping College Kids Cheat" by Dave Tomar. I found myself wanting to yell at the author many times for making such poor choices in his life, but all in all, it's a fascinating read.
And also: thesis mills
You can also order your PhD thesis online. Out of curiosity, I've filled out a request form twice. The first one got lost in my archives (I think I submitted the request late 2012, early 2013), but I remember asking for a quote for 100,000 words of a PhD thesis in 48 hours, with the topic of my PhD research (which includes experiments). They got back to me with a quote and a confirmation they could deliver the requested thesis. Ha ha ha.
The second time (November 2017) I filled out a request for a quote, I was limited to 10,000 words of PhD level work, to be delivered in 48 hours. Price tag: 275,175.95 British pounds. Again - I laughed in disbelief, posted about it on Instagram, and called it a day.
But some PhD candidates do take this route for their PhD thesis. Here you can read how a Turkish scholar pressed a paper mill for answering questions about delivering a PhD thesis, and he mentions the following jaw-dropping results of an investigation: "The Boğaziçi University Centre for Educational Policy Studies examined 600 post-graduate papers (470 master’s theses and 130 PhD dissertations) submitted between 2007 and 2016, and found that 34.5 percent of them were heavily plagiarised. The global average for plagiarism is 15 percent."
Another part of the underbelly of academia are predatory journals. These journals, following the open access publishing model, are only interested in cashing the article processing fee (APC), often with no or minimal peer review. While the general idea is that scholars are "tricked" into publishing with predatory journals, in some cases the authors know very well what they are doing, and use such publications to pad their list of publications.
Until 2017, Jeffrey Beall curated the Beall's list of predatory journals. Unfortunately, after receiving threats. You can find an archived version of the list here. By now, other players, including the anonymous "Stop predatory journals" are or were working on updated versions of the list, but many scholars are afraid of continuing this work because of the threats Beall received.
Sadly enough, predatory journals nowadays are the venue of choice for antivaxxer and climate change deniers to publish - resulting in these articles showing up as "proof" in a number of blog posts and news articles by these groups.
If you are not sure if the journal you want to submit your work to is legit, ask your colleagues if they have heard about the journal. Check some recent publications in the journal to see if these appear to be studies that have gone through peer review. Beware of emails addressed directly to you asking for a publication, especially when they talk about a (conference) paper you recently published. Similarly, don't accept invitations to serve on the editorial board of such journals (note that some predatory journals list academics on their editorial board who are not even aware of the fact that they are listed there - in case of doubt, send an email to the "famous" researcher on the editorial board with the title and abstract of your work to see if your work is suitable for the journal).
While less common than predatory journals, hijacked journals are according to Wikipedia: "legitimate academic journals for which a bogus website has been created by a malicious third party for the purpose of fraudulently offering academics the opportunity to rapidly publish their research online for a fee." Here's an archived version of Beall's list of hijacked journals. To my best knowledge, there's currently no up-to-date list of hijacked journals. When in doubt, ask around if you are submitting your work to the correct journal/website!
Ellis, C., Zucker, I. M. and Randall, D., 2018, "The infernal business of contract cheating: understanding the business processes and models of academic custom writing sites," International Journal for Educational Integrity, V. 14, No. 1, January 11, pp. 1.
Acknowledgment: thanks to Prof. Pacheco-Torgal for the inspiration for part of this article, and the links to a number of the articles referred to in this post.