Alan you need to think about something much better than a rug doctor if you really want to go out to folks houses to clean carpets properly. Easier said than done i know, as machines cost a fair bit, but, personally i would never consider a rug doctor for anything...
if money is tight, id look for a second hand machine off one of the guys on one of the forums.................................... ask yourself, jow often do you read of any of the cleaners on here using a rug doctor?? There is a reason!!!
It was a couple of years ago when I bought it, at the time I was looking at the Prochem Steam pro but for £1500 I wasn't sure if it was good or just entry level.
In the end I tried the Rug Doctor as believe it or not there were people using them for jobs with access issues where the larger Prochems were to heavy. To be honest I never soaked a carpet, I took my time with the spotting and on traffic areas got out the hand attachment and some elbow grease.
My main line of work is pressure cleaning and I'll hear people say £600 machines are rubbish, you need to spend at least £2000 and they would only by from x as everyone else sells junk. Truth is a £600 pressure cleaner WILL get the job done and if it's thought out and more time given the same result can be achieved.
With carpets I quickly realised that the Rug Doctor was never going to make money as the extra time spent wasn't viable. I've seen all the stupid comparisons of Truck mount v this etc, and I'm sure the guys with Prochems would struggle with the ridiculously dirty carpets and I'm positive anyone with sense would not waste there time cleaning them with a small machine.
It's not something I will be looking to invest in just now as I prefer working outdoors, but come the end of next summer I might rethink it.