Do you actually engage in this practice, or are you just spitballing from the sidelines, based on what you've read?
Because most people can relate horror stories of finding some janky "free" listing and they show up to the place and it's not as-described, and often gets weird. Or, they list something for "free" or cheap, and a stream of takers comes by, and again, gets super-weird because they don't seem to understand/care about the "seller" terms.
Perhaps there are "pickers" with a temperament for sorting through the dross and finding diamonds in the rough, but most of the "free stuff" seems to be like "come pick up this white elephant we can't be arsed to transport", and I can see a lot of wasted weekends and occupied storage space just holding crap.
I brought it up with my mom again yesterday -- she said her best friend's granddaughters love to "go thrifting" but thrift stores just ain't what they used to be. Due to Antiques Roadshow and eBay and Etsy and retail arbitration and American Pickers, every thrift store and "free stuff deal" is picked clean by some professional, before an amateur can put his boots on.
I actually do this and haven't had any real issues. You occasionally get someone who made a mistake or misrepresented something, but it's not too often. What does happen pretty often is having buyers flake. Sometimes you can weed them out by the types of messages they send. If on FB Marketplace, any profile created less than 2 years old, or if their rating is low, or if they send a pre-written message gets automatically ignored by me.
My biggest haul was a piece of 3/4" plate glass 4'x9'. I've never even seen them listed, but I would guess it costs thousands new. I got it for free.
Coincidentally my sketchiest buy was also when buying glass. The guy looked like he was on something and had the stuff on the 3rd floor of some kind of scrap warehouse place. Nothing bad happened and the glass was as described.