Any Contractor that you hire to install ceramic tile in your home should know the appropriate materials to use and proper methods of installing them. The Tile Council of North America publishes guidelines and methods of work based on extensive research and testing. Every tile Contractor should follow their recommendations. The installation of ceramic tile over a wood floor requires specialised construction starting with an analysis of the floor joists and subfloor to determine if the floor is stiff enough to support tile. Assuming the floor is stiff enough for tile, either a Cementitious Backer Unit (cement board) or decoupling membrane should be installed before the tile. Your wooden floor will expand and contract slightly with temperature and humidity, something the tile and grout will not want to do. Using a CBU or decoupling membrane allows a little 'give' under the tile that prevents the grout from cracking and the tiles from popping loose.
Showers, or any wet areas, demand certain methods of work as well. Nobody wants a shower to leak into the wall if a bit of caulking goes bad. To prevent this, a plastic sheet is fastened to the walls and brought down inside the tub lip or shower pan before the cement wallboard is installed. Done in this manner, the shower would not leak into the wall even if it was not caulked at all! There are also liquid membranes that can be applied to the cement wallboard to prevent water from ever moving into the wall beyond the back of the tile.
In short, a tile installation should not be judged simply by the way it looks, but by how it looks AND what methods have been used to make certain it stays reliably trouble-free.
Rick Anderson- Cell 317.513.3715