IMO, (for me) it's not so much as invading the others privacy it's free will. If you ask me (or any reader) what so and so thinks of you in a romantic way, or some other form of romantic relationship question, I think the tarot cards will give an answer.
BUT, the reading is about you, so IMO, your feelings will be the ones I can feel the strongest. We all have free will, you may ask if J has romantic feelings for you, and he may have, but J could also be in a relationship they want to stay in, where romance has sort of gone out the window, they want to work on it, but they still think of you and 'what if'.
If the reading is about you, it will show romantic feelings J has for you, will the rest also come up?
We all have free will, and J may be the love of your life, but J is married to a person and has a life J is comfortable with, no intention of 'rocking the boat'. Since the reading is third person, I'm not so sure all of this will surface.
Just my rambling thoughts lol, I think this is a very interesting question, would love to hear other thoughts.
I guess my question is, how much will tarot tell be about a third person?