Just My Opinion
Kirby Vacuums are a great product, and well worth the money you pay if you are willing to haggle a little on price.
Think about the money you waste on buying cheap vacuums, having your carpet cleaned, and having your carpet replaced. My mother bought a Kirby before I was born, and the thing could literally suck the carpet off the floor until the motor finally gave out when I was 16.
I bought mine 6 years ago, and the 15 year old carpet in my house still looks brand new despite four growing boys, several cats, and a dog. The Kirby does everything they show you in the demonstration and so much more.
I agree, door to door sales people and their tactics can be aggravating, but they're just trying to earn a living like everyone else, and its a simple matter of putting up a no soliciting sign and not requesting a demonstration in the first place.
The only vacuums that even begin to compare to a Kirby, in my opinion, are Dyson and Rainbow, and the jury's out on their longevity as I've never owned one or known someone whose owned one. I'll probably have my Kirby until I die, and maybe the same carpet, as well.