Interventionists worth their salt are highly trained, pedigreed clinicians that come with credentials and have close affiliations with a number of professional groups.  Some clinicians have years of on-the-job experience that should also be taken into consideration, but these folks ought to be credentialed as well. Please investigate the interventionist that you are considering hiring.
The two organizations to look into are the Association for Intervention Specialists (www.associationforinterventionspecialist.com), and the Association for Intervention Specialists Credentialing Board or www.AISCB.org.  It is unethical for an interventionist to receive remuneration for direct referrals to treatment centers.  If you feel that an interventionist has acted unethically, please put your concerns in writing and submit them to the Ethics Committee of the AISCB.