It's amazing how much dust can accumulate under chairs and furniture and in areas that can't be reached on a regular basis with vacuuming. Look at what a difference a good vacuuming can make...... This vacuuming was performed prior to cleaning the carpet.
The IICRC gives the following guidelines for vacuuming: Vacuum regularly. There is no step more important to preserving the appearance and long term usefulness of your carpet than regular vacuuming. Gravity and repeated foot traffic cause abrasive soil particles to fall below the surface of the carpet pile where they will damage the carpet fibers. Vacuum heavy traffic areas daily. Areas that are not heavily trafficked may be vacuumed two or three times a week.
Most any vacuum cleaner can make a carpet look good, but a good quality vacuum cleaner will remove the deeply impacted soil that you cannot see, but that is damaging your carpet. One place to check to see if the vacuum cleaner that you are interested in purchasing conforms to industry standards is the Carpet and Rug Institute. Go To www.carpet-rug.org for more information on vacuum cleaners that meet their rigid requirements.