Primarily I'm referring to companies that ask for "jack of all trades" security personnel but also 'require' highly specialized knowledge that I think they're unlikely to find. Some job postings leave me bewildered wondering where they are going to find people who can do that job and do it well. A hospital trying to hire a GP with many years of experience in neurosurgery comes to mind, I can't imagine there are many qualified applicants out there (edit: but the hospital may be trying to hire one person where two or more are needed).