motherearthnews.com
As someone who buys practically everything used, I am in many Facebook sales groups and hawk Craigslist almost daily. The one thing I see a ton of is upcycled furniture. Specifically, bureaus and vanities and such that have basically been refinished and had hardware replaced. Imagining you had the time and inclination, you could easily find yard sale pieces and turn them into something people want to spend money on. These things GO. If refinishing items is not in the cards for you, it can also be as simple as going out into the country and finding pieces at yard sales and flea markets that are lovely as-is, and then taking them to the city to sell at flea markets there!
Here is a more detailed account of someone who does this on a regular basis:
