Another thread (neighbours parking problem) got me wondering.
In my flat you can't see who is at the door (no nearby windows/or peephole) so I never answer the door if someone knocks (unless I'm expecting someone and even then I call out first to ask who it is. If it is just someone knocking at a random time and I have no idea I just ignore and pretend no one is at home.
I thought this would be what most people would do. Aibu?