Don't you hate those door to door selling?

I understand that people need to make a living. I don't really totally hate those door to door sales agent. But their scam tactics really makes me dislike them. One day, my father open the door to a sales agent who tried to sale us security alarm system. They told us that we been selected to have a free alarm system, and totally free. I just had skeptical question on how it gonna be free for us? After several questioning, they revealed that we have to pay the installation fee about $89.00. And they keep on pushing us to sign the subscription paper. We just rejected their offer. I don't like that they kept on saying it is free, at the end, you have to pay eventually. No thanks, not interest it this time.