fly-by-night

noun4

1. •
   A creature which flies at night; a nocturnal flier or traveler.
2. •
   [before a noun] One 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. •
   A person or business that appears and/or disappears rapidly, appearing untrustworthy, or giving an impression of transience.
4. •
   (disapproving) A traveling businessman or tradesman.