Here at Ed Young's we repair old faucets, and/or install new Tub & Shower faucets (or just shower only)
If it's a new faucet you require we need to open the wall either from behind the faucet (preferred) or thru the front (tiles?) -
most people don't know we have to get at the water lines that are in the wall to REPLACE the faucet.
Repairs are made from the front, not having to open up the wall.
Picture below shows a single lever type and a 3 handle type (to right) with center diverter for spout.