Floors supported by wooden joists will flex slightly.  With carpet this is not noticable, but with tiles it can cause the grout to break up and even tiles to crack.  Correct preparation and sealing of a substitute floor and use of the correct flexible adhesives and grout will ensure your floor retains its beautiful appearance.

"We were very pleased with the work you recently did for us in stripping, plastering and re-tiling the bathroom and toilet"  Jeanette and Maurice Bauld

Don't just tile up to your basin, cistern etc, but ask the installers to leave a short gap so that tiles can be slid behind for a more professional finish.  The units can then be tightened against the tiles to finish the perfect job, being careful not to overtighten and crack the tiles.