I should know, I was contacted by one of these "authors" who, for a fee, would put me in her book. I could then call myself "featured as one of the top 50 psychics and mediums in the country." Though it would no doubt direct lots and lots of "business" my way, I found it unethical and deceiving, and so I passed.
Don't be led astray. Ask around, look over the medium's training and experience. Call and speak to the medium. Hear his or her voice and make an informed choice of whether you believe that he or she would be the one to facilitate the best link to your loved ones in the spirit world. Not all mediums are the same and just like finding any other service or professional, honor your intuition and see what feels right for you.