I've been offered the services of lead generators, but for my business, they wouldn't work; they were in a call center in another country, wanting to cold call a bunch of businesses. That's not how I work.
In your business plan should be information about how you are hoping to attract and keep your clients. Make sure you stick to it! It is possible that head hunters work for your industry, and I respect that... But for my business, it would be a kick-in-the-face to my customers, and the types of customers I want to attract.
Another thing to be wary of is how will these headhunters know how much you charged a client, or that the client is the right fit for you? Will the head hunters get a commission everytime you sell work/services to that particular client? It seems very shady and vague as to what it would account to.
What I recommend is creating your own network, and using clients from there. Be it other freelancers, or just friends/family. Give them a kick back (i.e. a percent of the sale, a nice dinner, etc) for referring customers, but leave it at that. You are the one that then works on the relationship with your client, and you shouldn't need to be at a debt to someone else just to keep a client.