Regards to using a rug doctor type machines if you charge for a carpet cleaning service customers would expect that you turned up with professional kit and not something they could hire at a supermarket and do it themselves. Same goes if you turned up say to clean a block paving driveway with a diy type pressure washer I don't think they would be too impressed either.
Can you just imagine a customer geting two quotes to have their carpets cleaned and the other chap turns up with say a truck mount system and other specialist kit onboard that also happens to be properly insured, trained and qualified to do the work. I wonder who they would go with regardless if there was a difference in price quoted ?
I not having a go but just saying if you're going to offer a chargable service you need to invest in the right kit for the job.
This vid made me laugh
https://www.youtube.com/watch?v=g5TVf5nuq-8