How common is reference/citation padding? I recently discovered a paper of mine (pure mathematics) has been cited by a paper in a very different field (an area of applied mathematics) that I have nothing to do with.  The reference to my paper is used (along with another reference) to justify some statement in the introduction, but I have never studied anything like this (I don't even understand the statement).  It's clear that this citation is wrong, and while it's possible it was an honest mistake and the author was just careless, because the topics of the papers are so different (the titles are completely unrelated) and the journal and publisher are ones I've never heard of, it occurred to me this could be a case of dishonest "citation padding" (randomly adding superfluous citations).

Here are some possible reasons for citation padding:


Trying to legitimize one's work by adding references to reputable papers.
Either directly as part of a citation cartel to say increase impact factors, or as some indirect padding to help prevent a citation cartel from getting caught.  (I don't know if the latter happens, but this is part of my question.)
"Collecting dead souls" (i.e. some other nefarious scheme I haven't thought of)


Question: While I know citation cartels a real issue, is there any evidence that citation padding, outside of superfluous self-citations/citations within a citation cartel/ring, happens in more than just a few isolated cases?  For instance, are there stories of shady journals encouraging this or authors doing this systematically, like there are about citation cartels?

Note: I am not asking for a diagnosis of my specific case, or what I should do, which is discussed in these related questions:


How to react to your work being cited incorrectly or in a misleading way?
Should I do anything if I am cited for something that wasn&#39;t in my paper?
Not in my experience, but absence of evidence is not evidence of absence. This might require a genuine literature search using various keywords to give a quantified estimate for particular fields. I read citations quite closely in my field and I have only rarely seen this practice (&lt;1%). Much more common is slightly misrepresenting what the other authors said, or referencing something a reviewer might suspect the author hasn't read, like a tangentially related book used for a brief aside. And, of course, quasi-related self-citations.