There are two reasons why stains return.
The first reason is many stains are not just surface stains but the stain goes fairly deep. Examples of typical stains like this are 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 types 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 maybe 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 possibly a third time if required. Unfortunately, there is no way to try to clean this type of stain in one shot without running the risk of creating even more damage.
The other reason a stain may keep coming back usually happens when a homeowner 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 tips of the fibers. Once there, that residual carpet cleaning detergent can 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 is still having a problem, e-mail me at Alec@Alecscarpetcleaning.com and I will be happy to try to assist you.