Sold someone else’s couch that they left by the dumpsters

I’ve always done weird things to make a few extra dollars. And this one may be ethically questionable. A lot of people in my apartment building will leave things out near the dumpster including large items. The other day I saw a good condition nice leather couch. If I needed a couch I would’ve taken it. But instead I just posted it on Facebook Marketplace for $80 after it had been outside for a few days. Someone came that day and got it.