Can you rephrase this? I don't understand what you're trying to say.
The easy thing to do is to call to get leads of candidates you are calling:
"oh you worked for IBM, great company, I work with John Smith did you work with him?" "No i work with Jane Doe" "Where are you interviewing at the moment?" "Facebook, Google, etc" "oh I'm working the Facebook role did you meet with Jim? "no i interviewed with Sam" "was that through a recruitment agency or direct" "agency" (This last question is great news because it means that the company are open to using agencies and not just looking direct on job boards)
The list goes on, most people are clued up but we do this day in day out we are tricky with our questions and most people will eventually 'bleed' as we say
As a result, they will all back-stab each other in order to make their money... which comes from a surtax on your new employer, and thus reduces your bargaining position.
In the other direction, I've had the same person represented to me by multiple recruiters a few times. In all cases, the actual person was not at fault.
The questions are usually along the lines of, "I'd hate to be putting you forward to a company you're already communicating with, can you name them all for me please?". Although perhaps a little less blatant.