No way in hell would I allow it. But it never happened in therapy since all the therapists I saw were in private practice. Frankly I find it grossly unethical to even ask because I'm certain some clients don't dare saying no and it ends up being incredibly violating. I've had that happen with doctors and I said no way. But I know some people are too afraid to say no because they don't want to upset their doctor or don't want to come off as "difficult". It's manipulative. I'm not a guinea pig and doctors or therapists don't get to practice on me. I don't care about their training and if they want to train, how about they do it on each other?