We try very hard to be polite to any of the folks who are trying to sell their wares, because they are just trying to make a living. A smile and "no thank you" usually goes a long way, and some will even thank you and make small talk. As annoying as it can be, I would never just ignore them; that's plain rude. I've had one or two who wouldn't take no for an answer, but they're the exception and not the norm.