Bathrooms here are often among the most expensive rooms in the house, so how a repair is approached matters as much as the repair itself.
You may not need to touch the tile
This is where real money is saved. Many valve repairs can be reached through the existing trim plate, or through a small opening in the wall of the room behind — frequently a closet. Before agreeing to a quote that involves removing stone or custom tile, it is entirely reasonable to ask whether the valve can be reached from behind. Very often it can.
Custom tile cannot be matched
Stone, custom glazes and imported tile are effectively irreplaceable once a line is discontinued. Working around them takes longer and is nearly always the right call.
Scale on the valve
Hard water collects in the mixing valve cartridge, so the shower gradually becomes stiffer and less predictable until someone gets a shock when a tap runs elsewhere. Replacing the cartridge restores proper control.
Body sprays and multiple heads
Larger showers here often have several outlets on one valve. When one behaves oddly it is usually a diverter or a scaled cartridge rather than a fault with the whole installation — worth diagnosing before anyone starts talking about replacing the system.