Carl I would decide what cross-section of the market you want to aim at. If you want to do lots of low priced work for the "masses" you'll have to go about things a bit differently from if you're aiming at higher end clients. One size definitely doesn't fit all, but you can get a good balance without limiting yourself too much.
Low priced work will be mostly cash, higher end work will be bill in the post and politely wait for a cheque or bank transfer. 90% pay up almost immediately and it's worth waiting a week or two to pay in a cheque that could cover your month's mortgage

The thing about carpet & upholstery cleaning is that it is quite a significant outlay for a lot of people, and many don't have a set time frame in mind the same as something like window cleaning. People tend to want to call you as they think they need you, they don't want to feel pressured or obliged in to spending so much money at a pre-determined point in the future. Obviously this is where marketing to your list comes in. You catch them with a mail shot 12 months later and they'll respond (presuming you "won" them with your first clean).
Steep learning curve mate, and it starts as soon as you get to the "real world" part of the business
