Not terribly impressed by what I see here. Alignment of the corners is sloppy. As to the dark areas, can you feel any roughness with a fingernail? Can you carefully remove it with a utility knife? Hard to tell if it's something coating the edges or could be chipped.

I think he might not have cleaned up any morter that pushed up between the tiles. It will show up when grouted. As to the "green," tough to say....some sort of cleaner, perhaps?

Sorry you're having these problems. I would bring up these issues with the installer.

There is no doubt that the tile installer did a hack job here. Can it be improved on? Not really. Not unless you are willing to address the underlying issues.

If you are going to use rectified porcelain with small grout lines, everything from the framing studs out has to be exactly perfect. Which it obviously wasn't. You can see where the wall wasn't straight and the grout lines are off. It looks like he tried to trim the tiles to compensate for the wall's imperfections. That cut edge is what you are seeing.

If he wasn't involved in the wall prep for the tile, then he shouldn't have promised to be able to use those small grout lines. He should have explained to you that what you wanted wasn't possible without deconstructing the wall and then reconstructing it to more rigorous standards or changing your materials and spacing. But, would you have hired him then if he were honest with you? Would you have rebuilt the wall? Would you have accepted larger grout lines or chosen a different material? If the answer to any of those is no, then you kinda set yourself up for failure here by not educating yourself enough about the job on the front end to be able to know that a situation like this was pretty much an inevitable outcome of the parameters of the job as it was specified.

On the other hand, if he was involved in the wall framing and the total construction of the bath, then he is totally at fault here. Unfortunately, the solution remains the same. THe whole wall would need to be ripped out and redone correctly from the studs outward to get any real improvement here. For the immediate issue, the rough cut edge, if you hadn't used epoxy grout perhaps he could have popped that tile off and pumiced down the edge a bit to be more smooth, but with the epoxy grout, that's a no go without potentially damaging more than just that single tile.

You could very well be right, but frankly...I can't see the "wall" from the pic. If it abuts the wall, you're right. If not, my advice stands.

The wall behind the tile is wedi board so shouldn't it be perfectly flat?
I'll bring the problems up to the installer and see what he says about them.

They do have a grout stain. It may be possible to stain it and have it match, at least a lot closer. Is this tile recycled from a previous job? Trying to figure out why it is there in the first place. Are you sure it is not the thinset?

The tile is new. I think the white stuff may be from the manufacturing process??? The thinset is dark and shows up as the black spot in the picture, but that's another problem.
The grout is epoxy grout. Do you think I would be able to stain only the jagged bits?