This video illustrates the issues with renting a Rug Doctor Carpet cleaner to clean your own carpets. If you look at the dramatic difference between the two areas of cleaned carpet it shows you why a Rug Doctor carpet cleaner is not the best choice for cleaning your home.
Before I became a professional carpet cleaner in Tampa FL I used to rent the rug doctor cleaner at my local grocery store to clean my own carpets. It was laborious to use and not very effective at cleaning carpets. I remember going over the same areas slowing down my passes hoping that I could pull out more dirt and soil. The whole time I was just soaking the carpet more and more without getting any better results.
The real problem with these rental cleaning machines is they are not very balanced in their approach to cleaner carpets. To best carpet cleaning results you need to use a balanced system that uses equal components to clean. Those components are: water, agitation, time, chemical, and heat. If you have a cleaning system that uses all of those components equally you have a very powerful cleaning system. The Rug Doctor carpet cleaner uses a lot of water and chemical to clean the carpet but not a lot of the other components. An unbalanced system can easily swamp your carpet and leave a lot of dirt behind.
In the video the carpet looks grainy and dingy. That's because the carpet was not effectively cleaned and a lot of dirt and soil was left behind only to come to the surface as the carpet dried. The longer it takes to dry the more soil it will bring to the surface adding to the overall grey appearance of the carpet. If your thinking of renting one of these machines I would highly recommend putting your money towards hiring a professional carpet cleaner instead, You will get a much brighter clean that will stay cleaner a lot longer.