Got to agree that lower price doesn't necessarily mean poor workmanship. What it does mean imo, is that he's working for peanuts.
Used to do it myself for the first 20 years then got wise, now they PAY for quality, and why not, because they are happy to do so.
Carpet cleaners who charge little, usually do so because they think they can't charge more, and end up with repeat customers who expect to pay little the next time too. They are then in the trap of charging less then others, for fear of losing their repeat customers.
I was there too, but gradually escaped the clutches of customers who wanted a good job doing but didn't want to pay the correct amount.
It takes years to turn it around but it can be done.
Don't waste your time and effort on price shoppers, deal with those that will pay for good service.
Dave.