That corner is indeed a bit of a mess. Who knows why it happened. Were the trim pieces cut to that length (too short) or was that just-too-short-piece all the installer had when it came time to set it. Not wrapping returns? Doesn't know how? Has never seen or heard of it being done? Who knows. Slivers? Another ball of wax. Sadly, the installer might have been proud to have cut and set that thin sliver without it snapping.
I always have to ask the question, if someone does sub-standard work, why do they do substandard work?
1) Are they simply incapable? Write them a check for $1000, or a check for $10000. Give them a day, give them a month. Doesn't matter what you give them. They just can't do quality work. Do you want someone who is literally incapable of doing the work to do the work?
2) The installer is apathetic. It's just a job. Your work is simply another day at work for them. They really don't care. Doesn't matter how the job is done. "Done" just means done. There's a chance this person could do a good job, they simple didn't care to, because it's work. Sure, they should have done it right the first time. But what is "right"? Perhaps with specific direction, guidance on layout, expectations given ahead of time, this person could have done quality work. They're simply unmotivated to do so, because to them, it doesn't matter. It's just work.
3) Rushed. Short timeline. Must. Get. Done. Pressure from the GC? From the homeowner? So they got it done. It's okay, not great. Might have looked good when the tiles were set, but maybe they slumped, coming out of alignment. Maybe the thinset shrank, causing lippage.
4) Uneducated as to the materials they are using. Professionals are always learning. Reading. New materials. New membranes. New tile sizes. They know large format may need a certain offset, whereas someone who is "just doing the job" is dong nothing more than setting really big tiles, and it really doesn't matter how they are set. They're just big tiles. They might be capable of good work, and they do good work when the work is within their wheelhouse of skill and knowledge. But these are the guys that are shocked to find out, after the installation, that the large format they set, and that they set impeccably, now has impeccable lippage because they didn't understand the installation restrictions regarding the material they were using.
And on and on.
What it comes down to, is discuss with the installer why the installation does not meet your expectations. Or even the basic guidelines of tiling. TCNA standards, basic material installation instructions for the individual materials used in the installation, basic residential building code, etc.
Some installers will understand the work was over their skill set, refund a payment, and scamper off to their next day of labor.
Other installers will read up, and armed with new knowledge and a sense of pride in their work, and make it right.
Others will be ready for a proverbial knife fight if anything resembling "do over" or "refund" comes in to conversation.
People have already posted the links that have now become standard responses to threads like yours.
Good luck getting a satisfactory resolution.
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