Liquid spills such as coffee or animal accidents are notorious for wicking back up from the padding and resurfacing. This process pulls the spill / urine from the padding and gets treated to help prevent wicking back up.
If the spot comes back within 15 days of service we will come back and redo those spots at NO CHARGE.
In more extreme cases ( beyond just one little doggy accident spot) the sub floor may need to be sealed, and the tack strips replaced. Depending on severity the section of padding, and base boards may need replacing.
We find this to be true when the animal in mention heavily urinates in the corner of the room over and over. The urine then gets absorbed into the sub floor, tack strips, dry wall, baseboards, etc.
The material of your carpet has a huge impact whether the stain will release or not . Fibers such as Polyester seem to "hold on" to stains much more than Nylon.
In the case of that we use a STRONG Oxidizer (peroxide you cant buy at drugstore), and HEAT to add in an Oxygen Molecule to remove the stain. Depending on the age and condition of the carpet some faint outlines may stay or some color loss may occur.