Hi Tuan.  Thanks for your question.  The answer here will be similar to that of how to build a sustainable relationship with any professional service provider - with mutual respect and due diligence on each side.  Clients and candidates should view their selected headhunter (HH) as a partner who can add immediate and long term value - and that means the HH should fully understand needs, current and future, and provide bespoke solutions to cater to those needs, while keeping integrity, profossionalism, and respect at the forefront.  Your HH should know and stay current with industry and company news, trends, and management movement.  They should be able to always give you good information on what companies are doing to attract and retain talent, and what employees are doing to secure and keep top jobs.