Fun fact you can permanently scare off Jehovah's witnesses by offering them a random object and insisting that it's absolutely not cursed or possessed. Really insist that the thing you pulled out of the junk drawer is absolutely not possessed and is simply a gift that they need to accept.
Listen I know they're annoying, but the people standing at your door aren't the problem. It's the cult they're in.
Telling them there's a demon in your house is likely to cause them a decent amount of psychological distress. They literally believe in demons, they literally believe those demons want to get in to their home, and they literally believe it will destroy their life, get them kicked out of the cult, and separated from their only support network. Even though you and I know none of those things are true, (well, being disfellowshipped is a real thing) they believe they are and it's going to fuck with their head.
That said, they won't stop unless you scare them away, and that's probably the most harmless way to do it.
I bring them in, offer them tea and tell them what I think of the bullshit. After a few trips they come in for tea and we talk nicely about other things.
They used to, but since thrifting came into style, they mark up the possessed stuff to the point where you might as well go buy brand new possessed stuff.