There are two reasons why stains return.
The first reason, is many stains are not just a surface stain but the stain actually goes fairly deep. Examples of typical stains like this is when you spill a whole glass of a liquid or a slow leak from something that lasted for a while or even a pet stain.
Where these type of stains are relatively deep, they can require multiple cleanings. When a stain is cleaned, whether by you or a professional, you can only go over that area so much before you run a risk of over wetting and causing other possible problems. So it is best to clean up as much as you can that is visible in the face fibers. If it is a deeper type stain, the staining substance that was not removed and may be in the back of the carpet will usually get damp from the cleaning attempt and as the rug fibers dry, any remaining staining substance will rise to the top of the fibers, then become very visible. The next step is to simply re-clean this stain again and possible a third time if required. Unfortunately, there is no way to try to clean this type of stain in one shot without running that risk of creating even more damage.
The other reasons a stain may keep coming back, usually happens when a home owner tries to clean a stain and their attempt may be assisted using a carpet cleaner. Not being a professional, they usually will not have the proper equipment to rinse the area out and remove both the staining substance as well as the carpet cleaning detergent they used. Without removing this residual, as the carpet dries, both the staining substance that still might remain along with any detergent will rise to the fibers tips. Once there, that residual carpet cleaning detergent can actually attract surface soil from soiled shoes etc as everyone walks over the area. Before you know it, that stain seems to be back again. Sometimes by trying to clean that area the next day with just a little warm water and a clean cloth can often remove enough of the residual to prevent the stain from reappearing. To learn more about staining be sure to read our other blog on this issue. http://alecscarpetcleaning.com/blog/entry/stains-on-carpets
If you have a stain that keeps coming back and are still having a problem, e-mail me at Alec@Alecscarpetcleaning.com and I will be happy to try to assist you.