fly-by-night
Pronunciation:
noun
Definitions
A creature which flies at night; a nocturnal flier or traveler.
One who departs or flees at night in order to avoid creditors, law enforcement etc.
Example: Do not give your credit card number to that fly-by-night operation.
A person or business that appears and/or disappears rapidly, appearing untrustworthy, or giving an impression of transience.
A traveling businessman or tradesman.