Has your therapist been in therapy?
It's important! Has your therapist been in therapy? Your therapist may or may not have had issues with mental illness, trauma, or marriage trouble--but everyone has their "stuff." Does your therapist know what it's like to be on the other side of the office?
A therapist should be held more accountable than your average Joe for exploring his or her internal conflicts, because without self-knowledge (limitations, triggers, family history), a therapist can give you more problems than you came in with! Some therapists I have known, I am sad to say, use therapy to feel superior, or to prop up their ego.
I'm not sure why it isn't required in the training. I found when I was in graduate school that there was a certain type of student who seemed to be in school not to become a therapist, but to figure themselves out. They didn't arrive prepared. Thankfully, most of these people dropped out! And I hope they are seeking therapy.
"Have you been in therapy?" is a question you should ask any potential therapist. Of course it is unimportant to know details--and there is a another type of bad therapist who delights in telling you his or her sob story. But it's important to know that your therapist has explored in great depth how their development, family, or personality affects the way they do therapy. A therapist's self-awareness, especially having to do with values and beliefs, is critical to simply being able to listen to you impartially and empathetically. This quality is especially important for trauma therapists.
So ask! If a therapist gets sore about this question, or seems not to have time for it--go elsewhere.