Here's a little trick with head hunters. Their contracts don't mean squat. You can easily directly contact whoever you interviewed with and negotiate the headhunter fee back to your pocket. ( and make sure the sleezy head hunter gets nothing which is exactly how much they deserve )
Headhunters charge between 10-20%.
Just don't tell the "recruiter" and that's pretty much it. The head hunter may get mad, or they may threaten, but at the end of the day they're just a bunch of idiots with no clue, so they'll STFU and dissipate.
I don't like how recruiters are allowed to stalk people on Linkedin, in particular though. That's probably the worst part of Linkedin, and Linkedin loves those people because they are the main customers for premium services.