When I'm home, my door is locked all the time. I can see who is at my door and also talk to them through the door if they are a stranger. Nobody selling anything door to door is ever invited in, unless it's children selling something for school or girl scout cookies. If someone comes and wants to use my phone, it would be suspicious as I live out of the way from the main stream of people, and would not let them in.
A gun in the house is also good to have. A man came to my house late one night (many years ago) and wanted me to open my door so he could talk to me. I cracked it, but the safety chain was on (today I wouldn't "crack it"). He was a stranger and had some story about he needed lodging for himself and his family. I asked where is family was and he stated they were in the car. It was a stormy night and I could only detect one person sitting in the passenger side. What was weird is that the car he pointed to, was parked down the block, and not close to my house. As I was talking to him, my gut instinct was that this man wasn't on the up and up. I brought the revolver around from behind my back and let him see it at my side. That was enough to deter him and he left.
Something else.....I did tell him there was an unused motel on the back side of the block and he could stay in one of the rooms as it was in waiting mode for extensive remodeling (I knew the new owner), and there were still utilities on the premises (just in case he did have a family and they needed help). I told him which room was open. However, the next morning (early) I walked over to the old motel, and there was nobody there.