We discovered water damage on the floor and bathroom wall and found that the water was leaking from a pipe in the shower. Whenever we would pull the latch to switch the water from the faucet to the shower head, it would leak. We called a plumber who changed the faucet and said it was broken, but he didn't tell us how or why. He said that we couldn't have known it was broken. What causes a faucet to break? It was just replaced 2 years ago.

What causes a faucet to break?

Faucets don't break. At least not in the sense that you mean.

Obviously you had a leak. If that leak only occurred when the shower was used, it would have had to been either where the shower riser pipe (the pipe in the wall up to the shower head) attached to the valve, or where the shower arm (the pipe coming out of the wall) screws into the shower riser pipe. Repair of a leak at either place would not require replacing the valve.

Unfortunately you paid for a new valve you didn't need and the labor to install it.

I agree with Harold! I think you were charged for a new shower valve that you didn't need. The problem was not in a shower valve but in the shower riser. I will report plumber to the company that he works for all the city. Give champ the state information that you gave us. The answers that we gave you may help your case. Let me know how you make out. Good luck, Tom