One of the reasons that your carpets look dirty just a few days after you clean them with one of those rental carpet cleaners is because it does not possess the three aspects of thorough cleaning. As the image shows, there are three aspects of a deep clean.
Professional cleaners that truly care and desire to get your carpets, upholstery, or tiles clean will use agitation (scrubbing) systems in the cleaning process. Scrubbing loosens embedded soil and dissolves oils. There simply is no substitute for this aspect of cleaning.
Chemical (Cleaning Solutions)
The solvents and cleaners necessary for cleaning should be both thorough and safe. Harsh chemicals can do more damage than good when it comes to fine carpets, areas rugs, and upholstery. Caring professionals know this and only rely on the finest and safest cleaning agents.
It makes sense that the hottest water rinse is the best. Heated water will break down oil and dirt and makes them easier to extract. Caring professionals use high temperature (created by professional water heating systems) to thoroughly clean carpets, tiles, and fabric.
Many companies use the cheapest chemicals and warm temperatures. They don't scrub! Scrubbing takes times and energy!
I hope this post helps.
Kleaneasy Carpet Cleaning