Wicking is when small amounts of soil or stains left down at the foundation of the carpet, rise up the fibers of carpet while drying. This residue then finds it's way to the tips of the the fibers... right on top for you to be mortified by! Since I can only see the top of your carpet, no matter how thorough my cleaning is, I may not completely extract microscopic amounts of soil and stain residue left down below where I can't see them.
There are 3 ways to eliminate this problem. One is to take the proper time to clean and extract your carpet. The wetter a carpet is left, the more likely soil and stains will wick. Two is for the professional to use carpet fans to quick dry the carpet while the carpet cleaner is in your home. Three is shown in this video.
To help answer why soil and stains come back after carpet is cleaned in Broomfield, CO 80020 call 303-530-0646.