My front door is a left-handed door, that means the hinges are on the left-hand side as you are coming IN. When I open it from the inside with my left hand, it means my right hand is hidden by the door itself. Invariably, when I answer the door for strangers, it's with my left hand and my right hand already has a grip on my personal protection sidearm.
If an aggressive (read: assaultive) salesman were to try such with me, it'll be the last "hard sell" they ever have.
I learned to answer the door this way one winter when some homeless person was asking for the use of my phone, which we did not allow because of previous abuses by the poor folks in the neighborhood learning that we allowed so-and-so to use our phone and so we were always getting pestered about it. When I refused the homeless person, they could feel the warmth of our HVAC conditioned air with snow on the ground outside and they seemed to be determined not to lose that warmth. To that end, they stuck their foot in my door. Diplomacy is the art of saying, "Nice doggie" long enough to grab a big stick. Unfortunately, the big stick of my 12 ga. was just out of reach. I would have to let the door go, and hence allow the homeless woman into my home, in order to grab it. Being that close, I could smell her, and that only steeled my resolve that this creature was not getting in. Trying to cajole her to take her foot away so I could close the door, finally, I had had enough. Making like the shotgun was somewhere else in the house, I yelled, "Hey, mom! Could you bring the shotgun here?" That convinced the woman she'd rather be cold and alive than room temperature and dead. She left spouting curses, but I watched that she was definitely leaving my porch and property.
Now, with the sidearm always in my hidden hand, I no longer have to worry about this kind of scenario.
