Every year without fail we get the same guys showing up at our apartment selling "magazines". They say they're some poor kids trying to make their way back in life and whatnot, but the guys here before us warned us about them, just as the guys before them warned them (apparently they had paid for a couple magazines and never got them). So, every year without fail, one of us answers the door and talks to the guy for about twenty minutes. We get him to explain what magazines he has, what our options are, how much the magazines cost, and so on. The trick is that we know the magazines all "cost" $20, so we all say we can spare about $15. They try to get us to pay $20, and eventually we decide we can't do it.
Oh, but maybe one of my roommates can afford it; the one talking goes and gets the other guy, and him and the scammer go through the whole process all over again. By the time the third guy comes up and makes them go through the same thing usually they're pretty pissed off. At the end the last guy finally says, "so, we know you're trying to scam us. We've been through this multiple times already. Please get off of our porch" and walks off.
Although last year the guy ended up pulling a knife on us and threatening to 'cut us up' if we didn't give him some money... Probably not the best situation ever, but I'd heard what he was saying and when I walked up with my own set of knives (a couple buck knives clipped to my belt and sharpening a Ka-bar on a whetstone on the way up: he was carrying this basic 4" flip knife) and my other roommate came up with an aluminum baseball bat, the guy turned tail and booked it out of there. We called the cops after that, and the roommate talking to him was a bit on edge, but damn was it fun to see his face go from threatening to ghost-white "oh crap I don't wanna die, please don't kill me" pale in the blink of an eye. I will admit though, I slept with a shotgun under by bed for a few weeks after that, just in case.