Rinse out and keep rinsing until all soaps are removed.
Then using a cotton bud try the various products on very small areas to see what happens before diving in with a full blast of sod met etc.
All carpets are different by types, ages, wear, other products used on it etc so just because one person says "I had instant success with x" doesn't mean that yours isn't going to turn bright purple.
Remember under sell, over achieve is what makes you a god to the customer, so firstly tell your customer you are willing to give it a try but results could be very limited due to an attempt already being made by using fairey. If it doesn't look better you achieved what you warned but if it goes then ......