This video does a great job of explaining the pros and cons of professional carpet cleaning vs do it yourself carpet cleaning. As a professional carpet cleaner in Tampa FL I'm obviously biased toward professional carpet cleaning. It's my profession after all. This video clearly breaks down some of the obvious points about carpet cleaning and rental cleaning machines. I've used several rentals in the past to clean my own carpets so I can say I have through both processes.
I can't tell you how many times I've shown up at a customers house who has been an avid do it yourself carpet cleaner only to realize that it just wasn't worth it anymore. Comments like: "It's just too much work to do it myself..." or "It takes forever to dry and doesn't last very long..." I understand I've been there. It was my wife who introduced me to the idea of having a professional carpet cleaning instead of doing it myself. I was planning on cleaning the carpets and had even taken a day off work to get it done. That's right using a vacation day to clean carpets and save money. Thinking on it now I realize I wasn't saving money at all.
If you compare professional carpet cleaning vs do it yourself cleaning you realize it just doesn't pay to ad hoc it together with a rental machine. The actual cleaning results are not comparable. A professional with the proper equipment and training is going to out perform the do it yourself cleaner every time. If your thinking about the saving money by not hiring a professional watch this video and then call and get some professional carpet cleaning quotes for comparison. The cost is worth it.