I considered a franchise when i started looking at this trade, however when I weighed up the for and against options, I felt I could do it by myself and invest in some really good equipment & a nice vehicle.
I suppose its an easier option and I can see how that could be attractive, Chem-dry are the most famous carpet cleaning franchise, but in my area alone there are 3 chem-dry guys working in competition.
At the end of the day, there are many great training courses, some very helpful suppliers for equipment and chemicals not to mention sites like this that offer as much knowledge as you could hope for, so why pay someone else when with a little more effort you can pave your own way.
That's my advice anyway, unless of course your based near me, in which case I sugest you go for a chem-dry franchise!!