Sometimes you have to be very persistent, and that gets interpreted as aggression. For religious cults, diffuse charity collectors and similar it's usually sufficient to politely tell them they've come to the wrong person, and to leave the building and never come back. The electricity and internet salespeople otoh are extremely aggressive and I have often had to shout at them or physically chase them out of the building, and threaten with law enforcement. They shout back that they're trying to do their job but I don't see why that should make a difference. I'm in Germany, for reference.