sheesh. the purpose of doing the mud wall is so you can have a perfectly flat, plumb surface for you tile. that way, you'll have to bumps, or wavy, or crooked layouts.
In your 3rd pic in the comments, his edging pieces are wavy. does he not own a level?
A good layout takes a bit of planning. you want symmetry on both ends, and avoid any types of slivers or 1/2" cuts in the corners. Here is mine. we also did mud. And we spent hours doing the math in order to get perfect symmetry on the sides and around the accent.
As for the niche, what in the world?? why is the marble stained and why are his gaps uneven? look on mine and notice how it fits perfectly between full tiles. No sliver cuts. That's what you do in the planning stage when building the niche. you measure out your tiles so you know you need the niche so tall in order not to have to cut tiles lengthway.
in my top niche I used a solid piece of carrara for the shelf and the inner side pieces. Ditto for the lower niche. no shelf though. and I chose a mosaic. (which I have to say I had to fix myself. after the guys left for the day, they chevron was crooked in a lot of spots. I took out the pieces and reset them). Here's a closeup. I also used a gold Jolly metal edging for the inside, and black on the outer. this marble has to be sealed, or should be, before it goes in.
but take a look at the edge. see how straight? and we used a bull nose tile so you don't have to run the subways in a vertical line. cleaner looking
when doing a layout like these, whenever you come to a corner, the next piece on the adjoining wall, should look like the tile wraps around the corner. so that if you pulled it flat, all the tiles would be perfectly spaced and sized, with no slivers or choppy gaps.
look at yours and the diff from left and right. this is bad layout on his part. If he would have started correctly and measured, he could have had equal cuts on both ends. Plus, since that wall is most visible, he should have dead ended the tiles from the other wall onto that back wall so you won't see the jagged tile cuts.
Q