Dr. Smart, author of the bestselling book, Topgrading, recommends finding a good recruiting firm first, although he admits that is not always easy to do. Word of mouth references are best, he suggests.
There are national and state associations of professional recruiters that have web sites that can be searched by specialty, industry and location. These associations offer training, certification designations, and clearly defined code of professional ethics that speak to added value possibilities for the hiring companies and job seekers. The National Association of Personnel Services and the Georgia Association of Personnel Services is a good start.