When you get a reading, you are best served by being empathetic, not sympathetic. Brene Brown has a whole amazing thing about this here. Basically, you want to say, "i'm sorry that this happened" to your client without feeling their pain or being in crisis with them.
It's the whole thing about putting your oxygen mask on before your kids. You can't take care of people when you're flailing and you can't do good readings when they sink you along with the client. You have to practice this detached method of reading because generally, tarot readers are sympathetic folks. We're good at listening and relating and leaning in. It takes a while to learn your balance here, but the payoff is amazing.
Your clients will get a consistent reading from you. You won't walk away from the reading emotionally wounded. You won't cross any ethical lines or lean in so far that you obscure your purpose. Your job is to hand the person a reading. Their job is to receive it. Your job is then to walk away and let them deal with the reading.
One of the the things that helps me keep this boundary is actually visualizing it. When i read, i see my energy coming towards that of the client. Mine orange, theirs yellow, and the glowing gold we make together. When the reading is over, I take my orange and they take their yellow, and we walk away again.