The DBT National Certification and Accreditation Association (DBTNCAA) provides Certification as a DBT Therapist. While Dr. Marra is on the Advisory Board of Directors, DBTNCAA is a separate organization from DBTPsychotherapy.com. For more information you are highly advised to consult with dbtncaa.com for their full criteria and costs (currently $49 for the first year and $19 per year thereafter). They maintain a publicly available database of DBT Certified Therapists organized by State.
Please note that all of the workshops offered by this site meet DBTNCAA standards. DBTNCAA has additional requirements. Also note that qualifying courses and workshops need not be offered by Dr. Marra and may be achieved in any variety of ways (with Certificates of Completion from other accredited providers, and attestments on reading).
A basic summary is that a DBTNCAA Certified DBT Therapist must have 18 hours of training in DBT, 6 of which includes Skills Training. 3 hours of suicide/risk assessment training, have read two books on DBT theoretical orientation, read 2 DBT Skills Training Manuals, abide by the APA policy on Evidenced-Based Practice of Psychology (EBPP), have 500 hours using DBT on their client populations with weekly consultation/supervision, and use clinical outcome evaluation procedures in their practice.
All of these factors are clearly explained on the dbtncaa.com website. This website sells both a textbook of DBT theory (DBT in Private Practice) and a skills manual (Depressed and Anxious). The other requirements would need to be met through other providers.