So here's what you do. And this will be long. You meet with the installer and explain that you have multiple concerns. Tell him you expected when he presented himself as a professional, that he was going to perform this work in accordance with industry and manufacturer standards (as well as any local codes). Explain that you are concerned that his prep, prior to tile installation, is not in accordance with standards. If he disagrees, ask him to provide you with the standards he followed (TCNA Guidelines, ANSI Specifications, material manufacturer specifications for use in showers, including the Durock). Also explain that you expected if there was any question about the layout of the tile, he would have asked you first as the layout is not what you wanted. Further, the small sliver tiles are unacceptable (and they ARE unacceptable and also not in accordance with workmanship guidelines by TCNA). Ask him to tear it out, buy you new tile, and document and perform the re-do work in accordance to the standards. Regardless of his answer, follow up with a written recap of your expectations and his response. If he refuses to re-do the work, fire him without pay (and request a refund for what you have paid). Then hire a professional to do the job. Here's the thing, and I know this is long, but very important: The only way to reduce the unprofessional jobs is for the consumer to not ACCEPT the unprofessional jobs. There are thousands of us in the industry who are professionals and perform high quality work. We talk and we share stories like yours as examples of what gets in the way of the profession. We call them "tile fails" and there is even an industry site for sharing these (you should see the comments), and no, I'm not sharing yours. There is no job we loathe more than tearing out failed work and re-doing it properly. As for the cost. Someone mentioned 6k for labor. That's not unusual but it is location dependent. I'd guess 8K here. A 6k shower is not $80/sf in labor. There is a good amount of $ in proper prep & setting, and finishing materials, to start. Many of us do not charge by the square ft. We charge what we know will be a fair price for our labor and materials and level of craftsmanship. $70-78/hour for a pro is not unreasonable in our area. They do after all have insurance, taxes overhead, etc. and the right for a wage commensurate with their experience and craft. A helper or apprentice may be used at a lower rate for certain aspects of the job under supervision of the pro. Showers are more than floors, for example. Large format is more than a standard size tile installation. An upstairs bath or condo unit is more than main floor. You get the idea. There are variables. Tear out might be a day and 1/2 at $500/day. Don't forget disposal would be extra if no receptacle is on site. As for the comment above "jeez poor tile installer", no, not poor tile installer. Tile installer is responsible for confirming tile pattern before install. And the "sorry this is on you...relinquishing your responsibility", no, you didn't relinquish your responsibility anywhere but in the hiring process in that you hired someone who did not have the experience or credentials to do a professional job. Sorry you're dealing with this.
Q