In my experience you can't get away with it that easy. I have never had a sales person accept the first no. But if you know that your no is final then it really is an act of kindness to hang up instead of prolonging the agony and delaying the invevitable. I don't think you owe the same level of politeness to an unknown sales person you don't know any more than you owe the same level of politeness to a street vendor in a bazaar that is tugging at your sleeve to hawk their wares as you would to a friend. This is business and if you terrminate the call politely and quickly you free them up to go to someone who may be interesetd in their product and you to do more prodcutive work than talking to them on the phone. Rude is defined as not having or showing concern or respect for the rights and feelings of other people : not polite. I am always polite and I think is shows concern for their feelings to be honest and not lead them on when you have no interest in their product and no intention of buying.