What type of subfloor is required to support 12 in marble tiles? What do I check in the plywood and floor joists to ensure proper strength? If the floor an/or joist are not goo denough, how should I correct them?

I posted a previous thread about a problem, and every is fine. But now I noticed something else. I just had ceramic tile professionally installed in my bathroom. There is a 3/4" thick wood reducer transition piece between the bathroom and the hallway's wood floor because the tile floor is now higher. The problem is with a tile that butts against this wood reducer is flush with it on one side but slopes up to 3/8" higher on the other - creating a little tile "cliff" that looks like sloppy work. The reason for this is that over a 14" run of this tile the wood floor (& thus the reducer) slopes down 1/8" from left to right. This one tile slopes the opposite way (right to left) about 2/8". If this one tile was installed so that it was flush (or at least parallel) with the wood reducer it would look better. Would most professional installers consider this good enough? Or am I just being picky? The fact that is it quite obvious because it is in the doorway is my biggest complaint. Is is asking alot for them to replace/reinstall this one tile? Will it be harder to do the longer they wait? Thanks.