We have admissions consultants and sponsors who support SDN, post here, and offer some pro bono counseling (including blogs, vlogs, and ebooks). I also am supported and salaried by HPSA to provide pay-what-you-can advising but I have also worked for a company in the past on admissions consulting. I know the folks at the NAAHP Ask-an-advisor service too. There are a few others who are former prehealth advisors or admissions professionals who are independent counselors (a couple of them have an independent certification for freelancing admissions consultants, which I had never known existed or would be eligible for).
So those disclosures being said, it's like choosing a personal trainer. You should have specific problems or expectations to work on to benefit the most from any coach you are paying for their help. A hobby I can relate to is hiring a professional instructor to improve my [salsa] dancing technique... there are many instructors, so you choose based on the type of experience the coach has, the approachability of the coach, the teaching ability, and accountability for the cost you are paying for the coaching. Many amateurs or beginning pros may be available who would aren't pricey, but their expertise is not always based on their own experience.
Many are current medical students, residents, or junior staffers who are leveraging the fact they got in or served in an observer role on admissions committees. Some are prehealth advisors or application screeners.
In general the basic advice is universal and doesn't really change much. You can get this information from the AAMC website and reinforced by our website and articles, those of the individual schools/programs, websites from admissions consultants, websites from professional student organizations, and journalism outlets like US News and World Report. Some people are better in explaining things than others, or being creative. Some are more expert in writing, others in interviewing. In the end, it's about what you want to get out of the relationship.
[Reserving the "personal trainer" joke that came to mind... you'll just have to figure out which joke it is.]