Inside Job

And speaking of job ads (as I was in some posts last week), have you ever seen an ad for a faculty position, research scientist, or postdoc and been suspicious that the type or level of detail in the job description indicated that the department had an "inside candidate"?

I have found that this topic comes up quite often in discussions about particular jobs, based on reading (between the lines of) the job description in the advertisement.

Another suspicious aspect of some ads, leading some to wonder about inside candidates, is an application deadline very close to the appearance of the ad.

There are many possible explanations for unusually detailed ads and imminent application deadlines, and I think the existence of an inside candidate is one of the least likely of these explanations (at least in North America, the system with which I am most familiar).  (agree/disagree with this assessment?)

And yet, I know they do exist. I have written about this before, and described my own (now ancient) experiences with applying for jobs that real, not just inferred, inside candidates.

What I am interested in is: how common it is for someone to infer (without specific information) the existence of an inside candidate, based only on the job ad, and then not apply for the job?

Or: how common is it to know that there is an inside candidate, and have that piece of information affect your decision to apply (specifically: not apply because you think it is pointless)?