My father-in-law was a pastor (and a seminary teacher for awhile) for a mainstream church. So, when he'd get Mormons or Watchtower folks knock on his door, he'd try to convert them. Since he has a lot more education on their religion than they do, they're always at a bit of a disadvantage.
I pretty much take the same approach with most door-to-door salespeople whether they're selling religion or a vacuum cleaner. Most of the religious folk are very polite and thankful. The vacuum cleaner chumps are the worst. I'm not going to let the religious belief affect how I treat them. Now, if it comes up, I'm not averse to giving my opinion on things with which I disagree. I just re-explain to them that we may disagree but the water's free. I would hope that receiving "christian-like" kindness from non-christians would help promote some understanding in the world.
I don't have too much to add besides what Darkhorse already did, but I also was an LDS missionary from 2001-2003 (Bucharest, Romania). Hardest thing I've ever done, but definitely one of the most fulfilling things I've ever done as well. And, despite all of the rules about how you spend your time and whatnot, it's also one of the funnest times of my life, too. I would urge all of you when you run into missionaries (of any faith) to please be civil. If you know you're not interested, that's fine - but don't be a jerk unless they're being jerks first (and unfortunately, I know a few of them are). I know that those missionaries from the LDS faith don't see a dime for it, and I'm assuming that most missionaries from most denominations don't get paid for it, either.
I always make sure I have my water gun filled with vodka handy when they come to my door. I'm polite and civil at first, but then if they're rude or won't leave after numerous attempts to get them to do so, I bust out with the artilery. Only had to use it a couple of times...I think deep down, they appreciated it. Pugs
