Screening Minicab drivers
I used to have a large dog called Bonzo (The name has been changed, I don't want to give out my banking password. Ha! Ha!). He was a real softy and anyone could take him for a walk because he would obey their commands.
During his entire life he only ever tried to attack one person. I had called a minicab to deliver some kit and the driver had not even fully opened his door when Bonzo decided that he would kill him. I told the dog to go back inside but I realised that he had detected something about this driver that was not right. I looked carefully at this man, gave him the kit and off he went. It was worrying that this guy was driving around London, who knows what my dog had discerned?
Tl;dr Always travel with a dog