I don't get the business from adults as much as children. These kids are selling all sorts of sh%$ for "scholarships." They are either lying to me, or they are getting ripped off by the adults in charge of that crap. I asked one once what the scholarship amount was, and he didn't know. Another told me it was for $1000 or some low amount if they met sales quotas -- she wasn't specific as to what that was. I told both that they could make much much more money selling the stuff on their own. They both looked at me kind of funny and left -- which tells me they weren't smart enough to know they were being taken advantage of.
Very good advice, however sometimes impractical. We live in a safe, friendly neighborhood. The front door is usually open (glass storm door shut), with neighbors dropping by, kids in and out; half the time we're outside anyway. We can't see who is at the door until we're there. It seems awfully mean and rude to see it's someone we don't know, then slam the door shut.
If it's salesperson "season", I'll send my hubby to the door. He'll ask if they're selling something, ask to see their license, then tell them we're not interested. They're less likely to snarl comments at him.