Because I work in Sales I hear the words "not interested" more often than I would like. Fair enough. If I've shown the product, given you the pitch, and you're still just not gonna buy from me, then I can understand your position. Sometimes (unfortunately) people just don't want to buy something no matter how much it makes sense business-wise. I usually try to sniff these folks out beforehand, to avoid wasting both our times, but it doesn't always work. That's life.
What makes me snicker though, are these folks I call up, and before I can even introduce myself or what we do here, they tell me they're not interested. One has to ask logically, "how can that be?" I've yet to tell you anything, and yet you're not interested? What, pray tell, are you not interested in? Talking on the phone? Why'd you take the phone call?
Granted it's a great way to shut me down before I even get ramped up, and you're probably a piker to begin with, but you should at least do yourself the favor of listening to what I have to say before you tell me you're not interested in it. It just doesn't make sense to tell someone you're not interested when you don't even know what it is they're offering you. If nothing else, you should come up with a more grammatically and logically proper way to shut down the other person.