Really, when they make the effort, I am usually not going to be a monster, but regarding "decora" devices, the GFI is already a decora device. Over the years I have acquired and made many tools. It is not unreasonable to expect the Tile person to make a template that ensures a GFI will fit in the opening that they cut.I understand where you are coming from on this, but part of the problem is the decora device to begin with. Unless you are both there at the same time, I don't expect them to get the openings absolutely perfect for accommodating the trim screws of a decora style device. I have installed ceramic tile myself and that is not exactly an easy thing to do without the devices to check it out. At very least if you expect them to have it right for you you better let them know where there will be decora style devices, as they can do a good job on an install where there is no decora devices but it is a problem if you change to decora devices.
Do you expect drywallers or other other finishes to have same thing? Truth is they (usually) make a tight fit to the box also, it is just that the drywall has enough give to let you install the screws anyway. So I see it is that I have to install the offending problem more so than they do. If I have the box set so it will be ~ flush I won't ask for any more than don't block the box itself.