fly-by-night

Etymology:

• This is an old term which referred to an old woman who was assumed to be like a witch. Since witches are supposed to fly at night on their typical broom, the term was used in the same context for anyone who flies or runs away immediately from place or activity. The term was much used later in 19th century for business or people who used to run away or fly at night to avoid confrontation with creditors, angry customers and/or law enforcement after making (usually false) promises to their customers.