fly-by-night

/F L AY1 B AY0 N AY0 T/
noun
  1. 1

    A creature which flies at night; a nocturnal flier or traveler.

  2. 2

    One who departs or flees at night in order to avoid creditors, law enforcement etc.

    โ€œDo not give your credit card number to that fly-by-night operation.โ€

  3. 3

    A person or business that appears and/or disappears rapidly, appearing untrustworthy, or giving an impression of transience.

  4. 4

    A traveling businessman or tradesman.

Source: https://en.wiktionary.org/wiki/fly-by-night