Marble "stains" easily
If you are considering purchasing or already own a home with "real" (as opposed to cultured or artificial) marble, you need to realize that marble damages and stains very easily. When we moved into our condo, it had tiles that were polished beautifully and reflected like mirrors, but some of the tiles seemed faded or had imperfections in them. We assumed this was because they needed to be thoroughly cleaned.
For example, on the counter tops next to the sink, there was some fading and water stains. On the floor next to the toilet, there was a large stain that appeared to be from some kind of detergent. The tiles in the shower and around the bath did not have any reflectivity at all.
What we did not realize at the time was that these "stains" were actually etchings due to corrosion of the stone from the acid in water and cleaners.
We could not clean it
My wife didn't like the stains, obviously, and we noticed they would not come out when washed them (which probably created more stains). When we started to consider selling, we wanted to get rid of the stains to improve the appearance of the bathrooms.
The first thing I realized was that I didn't know for sure what kind of stone product we had installed. I figured it was marble, but I'm no expert. I looked up a few videos on YouTube and determined based on the look that we had marble. I wasn't sure if it was "cultured" marble, as I didn't know what that was.
It turned out we had "real" marble, which shines beautifully and has vein-like colors mixed in. Cultured marble is a mixture of resin and ground marble and can be molded. It has a small fixed pattern like granite.
My wife searched the internet for methods of removing stains from marble. She tried poultices with baking soda and cleaners and polished purchased at home depot. Nothing worked. I looked into it and realized that we might need to actually grind the stone to remove the etchings and get a polished look.
How we finally polished it
By searching around on the internet, I discovered a video on youtube by Marble and Granite Care Products that showed you how to polish marble with a small hand polisher, as opposed to huge floor polishers. They were selling a kit that included a polisher, pads, cleaning products, and an instructional dvd for a bit less than $500. If it were not for this product, I never would have made any progress in polishing our bathrooms.
It turns out that you buy several grits of sandpaper, and "hone" the marble so that it is smooth. We used 150, 250, 400, 600, and 800 grit levels. Then, you polish the stone with a product that raises the polish level to around 2,000 (it's a grit that gets smaller as the polish breaks down).
This worked! When I did a test on the countertop, it shined like a mirror!
Very hard work
Honing and polishing marble takes a lot of hard work - especially on vertical surfaces like a shower. It took me more than 40 hours of really hard work to do the shower alone. It's also more difficult to get the same shine level, because you don't have gravity pressing down on the polisher.
If you want to get a serious upper body workout, go ahead and polish your bathroom. But don't do it the hard way, like I did. I followed the instructions to go through basically 7 polishes on each surface. It was really hard. What I didn't realize was, if the surface was fairly good to begin with, you could get away with starting at a much finer grit level and get the same results in only 2-3 polishes.
When you hone and polish marble, you get water, marble dust, and grit flying off your polisher and landing all over your bathroom - walls, floors, fixtures, etc. This happens particularly at first because you don't know how to control the polisher.
I use a Porter Cable polisher you can get off Amazon that has speeds from 1 through 6. I thought that by using the 6 speed, it would polish better. I recommend staying at level 3. Level 6 will cause the buffer pad to wear out, fly off, and send particles flying. At level three, you can control the amount of debris flying off the sander and it's much easier on you and your pads.
You should definitely start out wearing eye protection and a mask, because the polish uses some kind of acid that turns into a nasty vapor that you don't want to breath in.
Once we got the bathroom all polished - it looks amazing. Nothing compares to it. The problem is, if a drop of water lands on the counter and you leave it there to dry, you get a nice etching in the marble. You have to dry any liquid off the surface.
To preserve the surfaces prior to selling and still use the bathroom and shower, I covered all the surfaces with Saran Wrap. This protects them perfectly. It's the only way I knew to keep them etch free, because you will never catch every drop of water that lands on the marble.
Don't get real marble
In my opinion, unless you are a cleaning perfectionist with OCD, I don't see how it's possible to have marble and actually use it. It's just not a practical product to have. Possible, but difficult. Granite is a million times easier to deal with in my experience, as it doesn't have the same problem with etching.