Tile floor breaking apart

[Bienes Raices]

I went to look at an REO and when I walked in I noticed that several of the ceramic tiles were cracked down the middle. When I started walking around there was a "crunching" noise even when I walked on the unbroken tiles, like they could easily break too. Obviously the whole floor needs to be redone. But is this usually just a sign of tile that was laid incorrectly, or low quality tile, or can it mean something is wrong with the foundation?