A dead 1950s radio is junk. The same radio, restored and quietly upgraded to play Bluetooth, is a gift someone pays hundreds for. Restoration turns nostalgia into a product.

People will spend almost anything on a painting of a pet they love. One artist went from ten-dollar Facebook favors to a full-time commission business, and the ceiling only goes up from there.

Model railroading is a graying hobby full of collectors who never learned to buy online. One operator built a multi-million-dollar store by being the person who did. You don't have to love the hobby, just out-market the incumbents.