We have polished carrera. Honestly, I haven't noticed any etching. Im sure it's there, so maybe its the lighting in the room. There's a small scratch on mine, we put a drill on it when installing window treatments. No one would notice it but me. I do occasionally notice a ring from the hand soap bottle or shampoo but it fades after a few days. We've been in the house for 18 months.

I selected honed carrara marble for my main/guest bathroom vanity top. I love it and I intend to use honed marble for my master bathroom when I get to remodeling it. Personally, though I like both polished and honed marble, I prefer the honed look. As porkandham said, polished is either more prone to etching or shows etching more than honed. If you do a search in the kitchen forum (and probably here in bath too) on marble and etching, you will find a ton of results. Basically, marble (and limestone and travertine) are calcium-based stones. Anything acidic (and I believe anything basic as well? - basically anything not pH neutral) causes a chemical reaction in the stone that we know of as etching. The only way to prevent it is to avoid contact with anything non-pH neutral. I would recommend testing all of your typically-used bathroom products on a marble sample so that you can see what etching looks like. You should of course also seal the marble to prevent staining, but sealing cannot prevent etching. Here and here and here are some pages from Granite Gurus discussing etching and staining on marble. I would also recommend doing a search in the kitchens and baths forums on marble and etching. A lot of people have asked questions about this and a lot of people with experience have answered.

Marble can be brought in either direction post-installation, honed-to-polished, or polished-to-honed. If this is DIY, going from honed-to-polished really isn't practical. Polished to honed is though. I don't recommend using an acid, it's too much of a wild card so to speak. If you have an random oribital sander, get some 600-grit wet/dry paper and have at it. Don't press hard, let the sander and the paper do the work. The grit may fill with marble, you can use a brush to clean it. As your grit wears, change the paper. The goal is to get an even covering of 600-grit scratches on the surface. Just go over everything equally, take your time, and you'll get an even matte sheen. And you'll save yourself the $6-$8 a sqft cost that a stone technician might charge. Honed is more porous than polished, so don't forget to seal afterwards.

I agree with Bill V--I noticed that even the action of pouring vinegar on the black marble tiles caused a blotchy look. When I 'honed' multiple tiles, I put them in a vinegar bath, so that all surfaces were exposed at the same time. After a set amount of time (5 minutes, I think), I rinsed the tile with clear water, then dipped it in a baking soda bath to neutralize the acid, and followed by rinsing again in clear water. Then wet-sanded and polished the tile to a finish that I liked. I used these tiles on a small counter, 22"x50", and used the scraps on a backsplash mosaic. Doing a kitchen with lots of counter space would be very time consuming. The carrara slab was an already-etched, second-hand find. Because of that, and the difficulty of getting an even etch without a 'vinegar bath', I used only the sanding method on it. The slab was too big for me to take outside, and even with a filter canister on the sander, it produced a lot of fine dust. When experimenting with etching, I laid a vinegar-soaked paper towel on one of the 12x12 tiles. It etched a really neat 'snakeskin' pattern into the tile. I've seen other GW members, experimenting with etching marble, mention the 'paper towel effect,' too. After I polished the tile, it was really neat--almost like a fossil. I loved it, but my husband preferred the smooth finish, AND I was afraid that if I had to sand out any new etches, the pattern would no longer look uniform. So I continue to use that tile as a sample beside my stove. LOL, Bill, haven't noticed any salad smell, but sanding produces a sulfur(?) smell. Also, I dropped some marble chips into a jar of vinegar, and grew some beautiful calcium crystals. If your kid is looking for a science-fair experiment, that's an easy one!