did the installer apply 1-2 coat of water impregnator to your marble (top, bottom and all sides) prior to installing them?
from the price i don't think they did. good water impregnator for natural stone like marble is very expensive ... around RM1500 for 20 litres.
the least you should do after polishing, you should get your marble surface sealed with good quality sealer.

when you apply water impregnator, it seeps into the marble. next time when you have water or oil spill it will not penetrate into the marble. it will remain on the surface only which you can then wipe away. otherwise, you will get stain which penetrate deep into the marble and impossible to remove.