​What business were you a part of or saw first hand that made an absolute killing ?

A friend’s parents owned a restaurant equipment supply company. They would sell new stuff to a new restaurant. Restaurant would go bust, they buy it back pennies on the dollar, resell and repeat.

They sold the business maybe 5 years ago, the guy ran it almost in the ground. They bought it back pennies on the dollar. Just sold it again last year. They have more money than they know what to do with.