Have any of you ever had your carpets cleaned that were thoroughly soiled? Did the carpets look extremely nice and clean when the carpet cleaner left, but a few days later some of the stains seemed to reappear? This is a process we call wicking back up. What happened here is whatever stain you had in that spot of your carpet was a deep penetrating one. Not only did it take the top fibers and sit up there, but also soaked through the backing and padding of your carpet.
In the process of us cleaning your carpet we got all of the residue off of the top of your carpet, but the heat that it takes to get those stains up also stirs up the residue underneath your carpet causing it to rise. This unfortunately can be an extremely big problem for your carpets. We can come back and clean the spot a couple times over(which you would be charged for seeing as it has nothing to do with our cleaning process but just has to do with how saturated that spot was before we got there)to see if it comes out but many times it will not.
You unfortunately would have to either replace your carpets after this or you could try to rip out the padding underneath and replace that then have us come in and clean the spot again. We hate when stains wick back up but unfortunately it is a part of our industry. The picture attached to this is the underside of a carpet and the padding just to show you what we mean by saturating through.(This is obviously a severe case).