I'm always envious when people manage to do this. When I go to jumble sales or junk shops, all I find is junk. I think finding treasures takes more time and patience than I'm prepared to expend.
However, when I did the makeover of my study this summer, I painted the old bookcase and chest of drawers. They were just the right size for the room and nice solid pieces of furniture that had once belonged to my mother-in-law. But they were sadly battered and marked with cup rings through misuse by the children over the years, but it seemed stupid to throw them out and buy new. They turned out just fine and now have a new lease of life.