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 r...