This. I live in a relatively small city, so I frequently see 3-4 different firms ping me on the same job. I'm the kind of person who feels guilty not sending a frendly no thanks. Usually by the 3rd or 4th recruiter on a gig, I'm able to respond with 'Oh, this is the <company name here> gig. Thanks, but it isn't a good fit for me.'
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.