fairchild:
I do not condone pestering anybody. Your example of the pesky salesman is good. Been there ... done that. They never bother me after being told 'no, but thanks anyway'. I give the same respect to anyone who says the same to me about my message. I do usually call on them again in about a year.
"Why go back?" ... circumstances change. People move. People change their minds
If they are still not interested, I leave on friendly terms. I'm not there to antagonize anyone. The whole point is to present an option for each person to consider. The witness has been given and my conscience is clear.