I'll let you in on a couple little secrets. If the rug has been shampooed or cleaned before, all you might need is hot water. Most of the time, too much cleaner is left in the carpet and it acts as a dirt magnet.
If you do need a cleaner, get a bottle of Tide HE Free & Clear laundry detergent. Use no more than 1/4 cup per TWO (2) gallons of hot hot water. Lay down a mist of the solution over a 4' x 4' area, scrub it in with a broom or the wand, then extract it using fresh solution and the suction on the wand.
Carpet is cloth fibers. Clothes are cloth fibers. I had one high traffic area of stains that was just not coming up with anything else I was trying. Tried this and the staining is totally gone. It worked where my professional chemicals were coming up short.
I must repeat, 1/4 cup per 2 gal is the MAXIMUM you want to use. Half of that concentration (1/4 cup per FOUR (4) gallons) is better if the carpet is not stained.