I've talked with a number of recruiters - 2 specifically indicated that they had arrangements with the end client - essentially an exclusivity deal. Once they revealed the client name to me, they'd let the client know, and if I made contact outside the recruiter, it was still an 'introduction' they'd get paid for if/when I was hired. Both of these were from a job search in the mid 2000s.

I've spoken with many more generalist recruiters, none of whom ever indicated this sort of system. I don't think it's overly common, but it was an arrangement that 2 recruiters indicated they had. Perhaps they were extreme one-offs?