Recruiters, as we know, make their living by sourcing candidates and placing them in roles with companies that are the recruiter's clients. This is why recruiters single-handedly work with prospective candidates and companies from the first interview to the first day and typically beyond.
It's no secret that some candidates use recruiters to gather knowledge on which companies are hiring, so they know where to submit their resumes behind a recruiter's back. It's a highly unethical and unwise practice, but it happens.
I've had a few brushes with candidate betrayal. While I prefer to trust candidates, I have worked with candidates who were wholeheartedly eager to use me for industry intel. Sometimes, I don't find out until it is too late – the company already hired the candidate.
However, BEWARE. As recruiters, we often have long-standing relationships with company hiring managers. We're free to disclose to the company that the candidate backstabbed us in the process of landing this role. This may often signal that the hire will be trouble down the line.
Moreover, we'll never work with the candidate again. I know the candidate is willing to betray recruiters, and recruiters I'm in contact with will likely know as well. It's one of the few means by which recruiters protect themselves. It's a small world, and it's wise to remember that.