There are a number of factors to consider when choosing a CranioSacral Therapist:
I myself am trained with the Upledger institute. I had to go through specific training and experience in order to put CST-T after my name. A list of qualified therapists in your area can be found here.
Word of Mouth recommendations from your family, friends and acquaintences.
For myself and many of the people I know, this is the first port of call. If you have a potential name - put the word out and see if anyone can recommend them or an alternative. It is always a good idea to google the individual as well - although, I often find that truly gifted therapists can often be non-existent online.
Referrals from other Healthcare Practitioners.
If you are pregnant or have a new infant - midwives and nurses can often point you in the right direction. Also, other complementary practitioners would be aware of good therapist in their localities.
Their Level of Experience.
Especially with the type of condition you are experiencing. I believe it is a good idea to speak with a potential therapist on the phone, ask them if they have treated people with specific conditions similar to your own - and then ask for a reference to check up on.
Your First Visit.
Trust and rapport are built up during a first session. You need to feel comfortable with your therapist. Being sceptical is fine - but in the unlikely case that something does not feel right for you - follow your intuition and find another therapist.