Several things weren’t considered in the experiment:

• A lot of people on the streets have some degree of mental illness or come from another background of vulnerability.
• he started the experiment im good health. Constant malnutrition is something that destroys someone’s hability to concentrate and think on complex subjects, and a reality for most homeless people
• A lot of homeless people have no digital devices needed to take things from a site and resell online
• No one in their right mind will trust a stranger from the streets to sleep in their van. He got this privilege probably by talking to someone and explaining his experiment or something.
• in a lot of places, there are no free things available to resell. Also, he probably already got this idea before starting the experiment.
• the site didn’t mention where he did the experiment, because a lot of people on the streets are subject to violence and live in constant danger
• and the most important one: there aren’t enough free stuff available for all homeless people to resell. If everyone tried this, the “market” would eventually saturate and no one would get a profit anymore.

I remember someone from here in Brazil that tried a similar experiment, but on a smaller scale. He started by buying a box of candies and reselling to people going through a busy avenue. Every time he sold all the candies, he had to buy more, getting just a small profit. At the end, he had to eat, and then spent everything, while being still hungry. The experiment wasn’t viable, because he didn’t even manage to end the day with more than when started. I tried to find the video to link, but couldn’t find it, unfortunately. But anyway, I believe this was much closer to the real experience.