What an interesting thread. Thanks Berenice for taking the time to answer all the questions so eloquently.

The reason we keep coming back if someone says they're not interested but doesn't specifically ask us not to come again is that attitudes/circumstances/householders change. The magazines that we most often present are released monthly, always with different topics - what appeals to one person may not appeal to the next. Many times people have said for years that they're not interested, only to have something drastic change in their lives, and they get to a place where they want to ask questions, and they become more conscious of their own spiritual need.
The repeated calling on the same houses even though people say they aren't interested is something I've never understood (and I admit it annoyed me). But now I totally get the JW point of view and understand what might motivate them to do this.