Headhunters are like real estate agents: they have really bad incentives i.e. poorly aligned with both/either parties that they are the middle-man for. So you get some that succeed (in scoring commissions) by talking to as many people as possible in the knowledge that there will be some false positive person-company matches. Those headhunters make a lot more calls so they are over represented in interactions.

If you want the really good stories talk to someone internal who has to deal with external headhunters. But everyone has some stories: I've been asked to sign ridiculous contracts (if you interview and get offered the job you have to take it) and seen some shady behavior ("if you can't pass a drug test I can help you with that.") Most people run away from those headhunters, but not everyone does and they are just playing the numbers game.

Unfortunately matching employers and employees is people-stuff and people-stuff is hard. If you can think of a better system please do (I'll be happy to visit your yacht).