I bought an old painting from my father in law for $30. Christie’s later appraised it at $5000. It was with a bunch of stuff he was donating to a charity and I liked it and bought it.
I recently found a Renoir being thrown away with a bunch of other stuff. I took a picture of it and sent it to an auction gallery. Turns out it was not a drawing but a lithograph and is only worth about $200. But always check. You never know.