Does it depend on how you have contracted someone (the tiler) to do the work?
If you have sub contracted the work out to him then I can see that the work is not up to an acceptable
standard and he should be given the chance to put it right and not paid for it until it is right.
But if he is hired as a temporary employee (paid per hour) then is it not the hirers responsibility to supervise the work to some extent so that the standard required could be achieved?
I don't really know the answer so just adding questions to the discussion.
I would note though that the tiling here is not what most tilers are used to - large format tiles fixed at (I guess) 22.5 degrees to the horizontal and needing to be cut around alcoves. If I was still tiling I would have loved it as a challenge but would have had to get a new cutter or two. I would also be charging a premium rate for doing it. So I hope the job was described well to the tiler before he took it on.
Some of the cuts to the alcove might be polish-able back to a good line although one looks to be short already. Those to the ceiling would need replacing though to get an acceptable ceiling joint (unless it is the ceiling running up and down!).
