The old rule of thumb is never to use anything you wouldn’t use on your hands. Never use powdered cleansers or abrasive pads to clean your stone. Even “soft scrub” type cleaners contain pumice, which is powdered volcanic stone, and might damage your stone countertops or floors. Never use any product which is acidic; this includes substances like ammonia or many common liquid cleaners such as WindexTM. You should always use sealers and cleaning products designed specifically for natural stone.
China has become the number two exporter in the world behind the italians (surpassing them some months, especially in granite), and is a powerful player in the stone industry, but the quality can range from excellent to terrible. The only full-proof way to assure high quality of stone is to have someone based in China that can interact with the manufacturers on a daily basis.