Two years later, I get an email from a headhunter who found my original resume. It led to my current job, which I enjoy a whole lot more. One thing to keep in mind is that the salary negotiation goes through the headhunter, and it certainly seems like they get additional money the lower of a salary you accept. So never accept the first offer.
That being said, its not in the recruiter's best interest to try to maximize your salary. The difference between you earning 90k and 100k results in a trivial commission difference to the actual recruiter. His interest is aligned with placing you as quickly as possible and moving on to another position. Its very similar to how your real estate agent isn't really motivated to get you an extra 5k on your 300k home.
Are you sure about that? AFAIK, they get a percentage (20%? maybe more?) of your starting (yearly) salary. So your interests (get a high salary) are aligned with their.
I assume they also have a clause in the contract that they get paid only if the candidate stays at the job for a certain period of time. At least that's what I would demand as an employer.