I agree Derek
This is where many carpet cleaners misunderstand the chemistry of cleaning. I recall In the past carpet cleaners saying to me, well I use XYZcleansit and it is ok not to rinse because it is a neutral pH.
Well yes it might be a relatively safe pH cleaning agent but pH and detergent residue are totally separate issues.
Eg. Washing up liquid is generally promoted as being kind to hands having a safe neutral pH. So does this mean because it is neutral you can pour this over your carpet and have no resoiling problems, NO!!! You would be left with a sticky soil attracting residue that foams up on cleaning and is very difficult to fully rinse out.
You can often discuss this with your client by likening it to washing your hair. You apply the detergent/shampoo, and then you rinse it out, common sense!!!
In my opinion the same applies to other professional carpet cleaning detergents, and the final process should be a rinse.
Just so long as you remember pH and detergent residues are totally separate!!!
I'll shut up now and get off my high horse!!! :
Regards
Robert Olifent