fly-by-night

plural fly-by-nights

1. A creature which flies at night; a nocturnal flier or traveler.
2. attributiveoftenOne who departs or flees at night in order to avoid creditors, law enforcement etc.

   Do not give your credit card number to that fly-by-night operation.

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

   Second, it will ensure that when fly-by-night providers go bankrupt, Medicare is at the top of the list of debts to be repaid. And finally, it will bring down costs by allowing Medicare to purchase goods and services at a competitive price.

   1998 January 24, Bill Clinton, Presidential Radio Address

   2 more examples

   The automobile industry rose almost overnight. Orders poured into the offices of companies already organized; new companies were formed by dozens, capitalized at millions of dollars. Fly-by-night concerns sprang up like mushrooms, flooded the country with stock-selling schemes, established factories where parts of motor cars, bought elsewhere, were assembled.

   1917, Rose Wilder Lane, chapter 22, in Henry Ford’s Own Story

   True, it was a good advertisement at Boosters' Club lunches, and all the varieties of Annual Banquets to which Good Fellows were invited, to speak sonorously of […] a thing called Ethics, whose nature was confusing but if you had it you were a High-class Realtor and if you hadn't you were a shyster, a piker, and a fly-by-night.

   1922, Sinclair Lewis, chapter IV, in Babbitt, New York, N.Y.: Harcourt, Brace and Company, →OCLC

4. derogatoryidiomaticA traveling businessman or tradesman.