Here goes--I do not intend to upset anyone, but-
I only use microsplitters, I only use cold water, I only use a top class portable.
I clean a lot of gruesome letting properties and very rarely have any difficulties with obtaining a satisfactory result.
The only thing is that you follow the directions and agitate well, and then some more. On really trashed carpet I use the white hard brushes, nothing ventured nothing gained.
Trevor