A sealant will repel staining agents but doesn’t make marble stain-proof. You can test if you need to reseal by dropping water on the surface – if the water no longer beads, it’s time to reseal.
Vinegar, citrus, and tomato will corrode marble; don’t let it sit on the stone. Wipe up spills immediately.
Avoid using acidic or abrasive cleaners.
To remove stubborn stains, use a poultice paste. Spread it onto the stain, then cover with plastic wrap sealed with painters’ tape. Once it’s dry (12 to 24 hours), scrape the paste off and wipe with a damp cloth. For deep-set stains, you may need to reapply paste.