How to say "No" to Salesmen

I have trouble saying no. Why does saying that kind of feel like admitting I am an alcoholic? Door to door salesman have always been particularly hard for me to say no to. A few years ago I printed a "No Soliciting" sign and taped it to the side window. It was such a good thing. I didn't have to worry about buying overpriced things that I didn't need, or hurting someones feelings and thwarting their efforts to have a better life. Then the sign fell off and I really didn't notice it was gone until a few days ago when a door to door salesman rang our bell. First he called me "queen of the castle", then told me all of my other neighbors who had bought his product, asked me what my first job was and where my work ethic came from....blah, blah, blah. He was good and it was freezing outside and I just wanted to get rid of him, so why not just say no? Instead I said "Okay what are you selling?" Magazines. I read a lot of magazines so I thought  at least it is something I will use. I pick out two magazines and he writes up a bill for me. $162. Are you kidding 2 magazines for one year? Oh well I didn't specify one year so that was two magazines for two years. What a bargain! At this point why, when I was outraged at the price did I not say "No" and go inside. Good question. Instead I said "there is no way I can buy two so I will just buy one." I then wrote a check for $84 for a two year subscription to one magazine. When I came inside I was so mad at myself. I couldn't believe I had just paid $84 for something I didn't need or want. My husband was home at the time and when he heard that I had bought something he could not believe it. I said "I think I can cancel the order but I have to send this receipt back in the mail and then in ten days they will mail you a refund". He said "give me the receipt". He then walked across the street and asked for the check back. I promptly printed another "No soliciting" sign and breathed a sigh of relief. This morning I googled "How to say No to salesmen" and they actually have some good ideas, but I won't be taking that sign down any time soon.