Honestly, everywhere I go I assume that professionals aren't up-to-date or adequate with the factual definitions and conditions listed the DSM, and I've never been incorrect about that assumption. Even the gender-mill therapists who churn out pills like butter only do so because they have an innate positive bias toward us; none of them really know what they're talking about either. I personally look for professionals who do have a very detailed, factual education beyond innate opinion, as somewhere down the line, anyone who bases their professional business on an "opinion", even if a positive one, and not a "fact", will hurt someone down the road. A therapist who lets anyone have pills, for example, is bound to come across a patient who wants to "revert" like it's nothing and then gets all suicidal about it.
Personally, my big thing is that if a professional disagrees with me when I know the facts are otherwise (ex. "Homosexuality/Transsexualism can be 'cured' by having self-confidence."), I believe it's a wise thing to say "Well, I will have to see what my lawyers advise about that diagnosis." (As literally every comment a therapist says about you is considered medical diagnosis, and if the diagnosis is wrong, it is considered fraud, negligence, malpractice, and defamation of character.) I have been to bully-therapists myself, and someone may think "if a therapist disagrees with me, I'll just do the mature thing and walk away while letting them take my money." - however, what's not being done in that case is sticking up for the other patients that very therapist may be causing harm toward; a discriminatory therapist may have already caused a suicide.
Many professionals simply need to be re-educated of both facts and laws, and I believe it's important in therapy to realize that the therapist is your employee, a professional who is being paid to tell you the facts; it would be different if the therapist was preaching to a congregation for free. At the very worst, a therapist or other mental professional may try to hospitalize you and frame you as someone in danger of committing suicide, all in attempt to stop you from transitioning. These things still do occur, and again, its why it's important to, even if it's not really true, to tell an out-of-hand professional that you have a legal team on your side. Therapists do assume that their patients are weak-minded people who will bow down to anything that they say, and when they do not have this power over certain patients, many of them become hateful, rude, and manipulating.