In my case, I got a referral from my gender therapist, who has gotten reviews and feedback from area trans people. She keeps lists of recommendations in various areas from attorneys to endocrinologists. If you have such a therapist, that is where I would go for the information.
The second point is, if you have a letter from your therapist stating that hormone therapy is medically necessary (required by a number of endos and insurance) and you have an appointment with an endo, then it would be a breach of ethics to do anything than treat you like a woman with a hormonal imbalance (which, really, is what you are). Endos shouldn't be concerned with genitalia other than the effects they have on hormones and vice-versa.
So, if you do have a letter, then I would suggest you not worry about it at all; if their questions get too evasive you can always say "That is confidential, between me and my therapist" and leave it at that. You are a human being who needs medical treatment; remember that. You are worthy of dignity and respect, despite what society and anxiety have done to you (and us) over the years. Be polite, but be firm.
*hug*
*Edit: If you are going to an endo without a note from your therapist, I would imagine you would need to be more forthcoming to demonstrate you know what you are doing and reassure the endo your consent to the treatment is truly informed.
