What is fly by night?

"Fly by night" is an idiomatic expression used to describe someone or something that is unreliable, deceitful, or shady. It is often used to refer to shady businesses that operate under the cover of darkness or lack of proper documentation or licenses. The term originally came into use in the 18th century to describe people who operated as thieves or dishonest tradesmen who would settle bills on their way out of town before the victim was aware of their scam. Today, the term is commonly used to describe businesses that operate in a transient or shady manner.