As a professional carpet cleaner in the greater Tampa FL area, I get asked about carpet cleaners all the time. My customers want to know the best way to clean minor spots and spills on their carpet and upholstery. I tell them that most spots can be removed with simple room temperature water and a wet dry vacuum. I honestly can't remember how many times I have I removed spots in my own home with a small 2-gallon wet dry vacuum from Lowes.
The video above reviews three of the more expensive carpet spot removers. As expected all three worked well on the spots with minor differences between them. They all spray cleaning solution and extract with and cleaning tool attached to a vacuum. I tell my Tampa FL customers to ditch the cleaners that come with these spot removers and just use water. I go even further and tell them not to fill the machine at all. You can get better cleaning results by pouring water on the spot you want to remove and then extract with the carpet cleaner.
If water alone doesn't seem to be doing the trick then you can use a mild soap to remove the spot. I recommend about 4 drops of dishwashing detergent in 8 cups of water as a cleaning agent. Pour it on the carpet and let it sit for about 30 seconds to 1 minute. Then extract with your spot remover. As a professional carpet cleaner, I recommend going to your local hardware store and buying the smallest wet -dry vacuum they have. It will work just as good as the ones in the video.