Beware of the three most common ways do-it-yourselfers (and inexperienced pros) damage carpets:
Over-shampooing occurs when either too much shampoo is used or the carpet is not adequately rinsed. Both are practically inevitable with some wet do-it-yourself approaches. This is the biggest reason why even hard-core do-it-yourselfers should occasionally use a professional. If they don’t, the build-up of soapy residue can be impossible to clean out, leaving a carpet that is a virtual dirt magnet.
Over-wetting occurs when too much water soaks into the bottom of the carpet. Some backing materials cause the carpet to discolor if they get too wet. Some carpets will shrink, literally tearing themselves up from the floor. If the backing and pad get wet, it is very difficult to dry them, and you run the additional risk of mold and mildew problems.
The final carpet-cleaning hazard is stains caused by furniture coming into contact with wet carpeting. Many kinds of wood furniture will release some of the dyes in their stain if left in contact with a wet surface. Many pieces of furniture have feet that are at least partially metal. The metal can rust, leaving a stain in the carpet.
Do-it-yourselfers are more likely to encounter these problems because they often don’t remove all the furniture from the room when cleaning, and they often don’t have ready access to the foam blocks and foil-backed cardboard squares that the pros use to keep the furniture off the carpet until it is dry.