What sort of condition is the carpet in? If it's OK, then a dry compound clean preceded with a fine mist of microsplitter may well come up trumps.
When filthy, I have extracted these before but to be honest if you were going to attempt it, a twin vac porty is out of the question. You need much better vac performance, like a triple vac machine or a truckmount, both run with the pump turned right down so you get a high vac to water ratio.
Obviously not in the training manual, but works if you know what you're doing.
I extracted a sisal carpet once without realising what it was. Never did it any harm, looked beautiful when it was finished and I've extracted it twice since
