losthobbit, in many cases, participating in a conversation with the witnesses when they come to your door might lead them to believe there is some degree of interest on your part. In other words, they'll make a point to come back again and again. However, this may not be so bad if you do enjoy conversing with them.
It also depends on the individual witnesses. For example after going door to door for an hour and either finding no one home, or having a few homes where people were nasty and told me to get lost or to go to hell, if I came across a friendly person, I would welcome the little "break" and not want to ruin it by being too pushy. I know of other witneses who would do this too. If the householder had a classic car, we'd chat about that. I'm a dog lover and naturally would chat about dogs if there was a dog there. Some people would just want to ask us about our beliefs, but are not interested in the literature. I figure, we are neighbors, we see each other in the grocery store and around town, why not be friendly and interested in others in the community?
Other witnesses I knew would only want to get to their point, and if you didn't want the literature they would leave. They're on a "mission". Maybe that type is not worth talking to anyway.