A beautiful tile or flooring installation without the proper prep work is a failure.  It may not show up immediately but could cause major issues down the road and by the time these issues show up the damage is already done and could be extensive.  For your tile installation project, you want someone who has experience and knowledge of how to install tile correctly, without taking shortcuts, while ensuring that the final installation looks beautiful and performs as it should long after that installer is gone, someone with the proper skill level to do it right the first time.
You want to hire Qualified Labor.

​From a technical perspective, qualified labor means having successfully demonstrated a tile installer’s skills that meet tile industry standards and best practices. That is what the Certified Tile Installer (CTI) program does. The CTI designation identifies the professional installer who has reached a level of proficiency to independently and consistently produce a sound tile installation that displays good workmanship.