People should send calling cards ("Hi, it's so-and-so, wish to call on you at your convenience") and wait for a response. Same for telephones (send an email/text message first).

Same here. Anyone at my door who I don't expect is either proselytizing for their religion (looking at you Mormons and JWs), begging for money, or trying to sell me something.

I think the most common unexpected caller for me these days is a delivery person asking me to take in a parcel for some neighbour who isn't in...