Years ago, I lived in a city that decided to offer a "garbage collection amnesty week". For one week (with your regular pickup day, Monday-Friday), you could put out as much garbage as you wanted at the curb, and it would be collected for no extra charge.
The city apparently vastly underestimated how much garbage was going to go out. It was not all collected that week. There was junk sitting out on the curb, all over the city, for 1-2 months.
There were also people driving around, searching for cool stuff. For example, one of my items out on the curb was an old bird cage. One morning, the bird cage was gone, and there was someone else's old doll house in its place. A friend of mine found a complete metal suit of armor; not really functional, but a nice decorative piece.
There can definitely be value left in someone else's trash. But if ordering on Amazon, as a paying customer, I would at least want to know up front if I'm buying something that came out of the trash, and make my own decision on if I wanted to buy it or not.