Wishful thinking
Each year people get hit up by a service provider printing postcards, often done by kids that are living in shelters. It's not a bad thing, but the fact 'is' cards done by kids living in a shelter have higher resale value than something pawned by a vagrant on a streetcorner.
The funny thing is I've never 'known' a homeless person to be pawning things on sidewalks. The majority of times I've seen people locally trying to hawk items...it was the same people, in the same location, selling the same thing. Often times they'd be hanging out and around the actual homeless until their work was done, only to head off to their own homes.
Most often I've seen people 'buy' their way into homeless circles on the street. Buy a few cans of beer and chips for two people on the streets, and you've got loyal bodyguards for at least the day, if not retaining them for future 'possible' days. Sometimes it's not hard to spot them.
Generally the social engineers can be found in any group outdoors, they're usually the most animated, charismatic, and loud...and they're the ones that really don't care if one of their peers ends up in jail if scuffles start up with others regarding their behavior.