Seamless marble floor problems expected?

I have a contractor installing diamond pattern, seamless marble floor tile for bathroom in our events hall.

Inspecting the first section he installed, I see:

1)There are gaps between some tiles. Up to one millimeter thick.
2)The corner where four tiles meet may not be lined up perfectly like a cross.
3)Tile may be around one millimeter higher than its adjacent tile. Running fingers across tiles I can feel the incongruous bump.

I brought up the issues to him. He essentially tells me:

1) and 2) are due to each tile's imperfection, not being a perfect square. He lays each tile in a box indiscriminately without discarding the imperfect ones.
3) is due to shrinking of the mortar.

He is willing to redo them. But he wants me to select the 'perfect' tiles for him to use for the job, and watch and approve him install each piece. Is this unusual?