Yes, you need to have your marble vanity sealed with a good quality penetrating sealer as it is a soft, porous stone. Unsealed marble will absorb liquids, which will lead to staining. Although sealing your stone with a penetrating sealer will not protect it from etching it will protect it from staining and it will help preserve the look of your marble for longer.
A penetrating sealer is recommended instead of a surface sealer as a waxy surface sealer will sit on top of the stone and eventually become scratched and dull. There are now film type applications such as Tuffskin available to protect the stone surface from etching.
Natural marble contains a variety of minerals that can react adversely to some supermarket cleaners. These cleaners can disturb the delicate PH balance of the minerals in the marble and destroy the look and feel of the stone. Some supermarket cleaners contain citrus or vinegar are acidic and can etch the surface of the marble.
Specially developed marble and stone soaps and cleaners are PH balanced and designed to gently penetrate the porous stone surfaces and lift in-grained dirt. To avoid damage to your marble benchtop and other stone surfaces use only recommended products.
Most scouring pads especially the green type will scratch the surface of natural stone and damage the glossy finish. It is best to use a cotton mop or micro fibre cloth to clean and polish your marble benchtop as these are gentle on the surface and will not scratch.
If scouring is necessary to remove stubborn stains, use only professionally recommended products such as the Scrub A Dub white scourer and follow the directions given by your stone care professional. Change the water regularly when rinsing. In most cases stubborn stains and discolouration may need to be removed by professional polishing.