What is it you hear when I say "Not now, I'm not interested?" Is it akin to the wind rushing through the trees? Does your mind translate it as "I am playing hard to get, so try harder! No really, I am very interested, I am just walking in this direction and pretending I have something else to do and am not looking to re-hash my cell phone plan?"
For future reference, the correct response is NOT "Miss, oh Miss, can I just ask you one question?" Thereupon you should NOT convince the busy and disinterested-looking shopper to come over and shake your hand whilst you introduce yourself. And the wrong thing to say - this is where the whole "I'm not interested" thing becomes key, becomes absolutely crucial - is "Miss, how much are you paying for your cell phone service?"
Of course, having studiously done all of the above, despite these things being the Wrong Things To Do, her reaction will be an exasperated roll of the eyes, followed by a clipped "Not NOW" as she turns her back on you and proceeds to her destination. It does, for future reference, only make things worse to shout after her, "But you could save a lot of money!"
The customer is not interested in your sales pitch. She is not prepared to listen to you, and will in fact refuse to do so. She is tired, rather hungry, has just spent the last of her physical cash on stickers for the recipe books, and only wishes to ogle the sparkly doodads at Claire's before making her way home to her lovely significant others. Re-negotiating a cell phone plan is nowhere close to the fore of her list of priorities.
Love and kisses,