I think with some wool carpets you need a bit of confidence that once they dry they will look better, you can't judge them on how they look straight after cleaning. Wool can darken when wet so in traffic areas you can over wet by trying to clean out dirt that isn't there...... it just has the appearance that it is still dirty because it's wet.
If it's a wool carpet and really bad I treat it as any other fibre, the customer wants a clean carpet not for you to give him excuses about..,......." its wool so I need to use mild cleaners, that why I haven't got it clean"