My flat has a pale green, old -but obviously extremely expensive carpet throughout. Really throughout, bathroom and en-suite included? My daughter, who collected the keys on the day I move din did manage to get rid of them in those two rooms. However, the rest had all sorts of stains and marks on them. Some looked like oil stains, not sure what others were - little black spots,etc.
Anyway, do not wish to re-carpet for at least a year - so have spent some time working on those - using a combination of my Vax Carpet cleaner and a separate steam cleaner. They are all gone now, some did take three of four times to get rid off, but the carpet does like new now throughout - and the added benefit of knowing it is really deep clean.
I know the vendors did have a professional cleaning company in as the flat had been empty for sometime before I moved in, but think these just vacuumed the carpet, not a carpet cleaning firm.