if they are really bad use emery paper followed by scotch brite to remove marks and scratches. to get them to a bright finish you need a pollishing mahine with a cloth mop with plenty of polishing soap. all should be avalible from an enginneering mearchants or machine mart. the best thing to use as a final cleaner and to remove finger marks is baby oil, its cheap and its as good if not better than and other stainless stell cleaner on the market
Cream cleaner, or equivalent, and water. Much better and much cheaper than cleaners sold for the purpose, like Autosol. In the Med stainless develops corrosion pits quite quickly. Cream Cleaner twice per year keeps them well polished.
you can get asomething called pickling paste from a welding suppliers. it cleans and decontaminates stainless steel but be careful its acidic and will burn.