mm wrote:
I was visiting my brother and they have 12" ceramic tile in most
rooms.

A lot of the tiles are about a half millimeter higher or lower than
the one next to it. Maybe less, but I can easily feel the difference
with my fingers, and when pushing a dresser, the dresser has to be
lifted up to get onto the next tile.

Is this work within professional standards?

A half millimeter? How did you measure that? Basic of tile
installation is to use a length of 2x4 or whatever to tamp newest-set
tiles so that they are level with and at the same level as adjoining
tiles. Saw a neighbor going through great pains to set pavers in cement
on a concrete sidewalk - used a level to make sure each paver was level
as he went. Every paver was precisely level, just not the same
level....a little higher, a little lower. Can see it clearly. He
claimed to be brain damaged from falling off roofs when he was an
alcoholic. There was no "was" to that part of the story )