Cleaning marble and tiles...?

I am cleaning for someone with a lot of marble etc in the kitchen and also have a tiled bathroom or three. Using a Selleys product at present but its not making much difference. The floors look terrible. The benchtops in marble are stained and marked badly. Has anyone got any suggestions? I would love to get these looking as good as possible for them.

monkey_room, I'm not sure re what's best for cleaning the marble but for the tiles, have you tried good old vinegar?
When a friend had floor tiles laid she was advised by the tiler to use only vinegar and water to clean the tiles because vinegar doesn't affect the colour (if any) of the grout.I heeded this advice with the floor tiles at our front door and it works prefectly even when the area is quite grubby as it is prone to be in the winter with wet/dirty footwear.For great results I just use a generous quantity of white vinegar in hot/warm water and a good old sponge-type floor mop + if very dirty, a scrubbing brush.

Hope that helps.:-))

Thanks 245sam, I am unsure with these ones as they are a special stone and seem to have a lot of staining appeared on them where any kind of product has been dropped or used. They are less than 5 years old and are really damaged.(Mental note to self never get expensive tiles or marble in house) I may try a small amount on a hidden area.

Google it, you will find Vinegar is a no-no, and alot of other products too as they eat away at the tile.

Yep it has to be ph neutral. Marble needs something like tin dioxide to polish it and to take out stains its peroxide. I wonder why people get the stuff in their houses? It is almost impossible to maintain.