1st A polite no thank you.
2nd Reinforce that fact that I have said no, telling them that if i have to say now a third time I will not be so polite.
3rd Be as rude as I like point out that they were warned and if they don't like it they should have listened on the other 2 occasions they had the chance.
You would be amazed how many times I have got to number 3.
Also point out that the ability to sell also requires the ability to listen.
We had a guy who dropped of the Avon catalogue, he was never asked to do so, a couple of times we had just put it in the bin, one day he saw me and asked me for it and when I told him that I didn't have it he proceeded to moan about he he needed it and questioned why we had done so.
I then pointed out that we have never asked him to drop one off, he just kept whining that he needed, at this point I got the hump and just came out and said that I didn't have his magazine and that was that.
This wasn't enough for him, he was going to mark us of his list, a list we didn't ask to be on, a list we didn't want to be on but before he was prepared to do that he needed the catalogue back.
Well at this point he got told in no uncertain terms to go away.