1) Registered with professional body
The first thing to always is check when choosing a therapist, are their professional qualifications and professional body registrations. There are different registers that therapists must be a member of in order to practise. I am a fully registered member of the British Association of Counselling and Psychotherapy (the BACP), the largest body.
Every therapist should be committed to their continued professional development. Feel free to ask how they have expanded their range since qualification. In my case, I have continued to develop my skills to work with trauma, grief, young people and gender specific issues in the last couple of years alone.