"There are various products with this in, Craftex and Chemspecs coffee stain removers are both based on this in liquid form. Powdered versions are Shift and Spray n Go. The beauty of the powdered ones are that you can alter the strength to suit. I used to remove stains for the insurance industry and used to get a 75% success rate which is about the norm. Don't expect to get out every stain, especially if the customers messed about with it.
Spray n Go is designed to be sprayed and left, however this is an American product where the vast majority of carpets are manmade. It is a bleach and can lighten wool carpets so be carefull. I used to mix it up hot, spray it on with handtool at the ready and them whip it out once it had achieved the desired result. If there was a slight discolouration remaining I would mist with a weak solution and leave it. "
Thank you Johnj ust read your post,
Somebody who does know what they are talking about
Geoff