fly-by-night

unreliable and shady

Synonyms: brief, cowboy, disreputable, dubious, ephemeral, evanescent, fleeting, here-today-gone-tomorrow, impermanent, irresponsible, momentary, not to be relied upon, not to be trusted, passing, questionable, shady, shifty, short-lived, slimy, slippery, temporary, treacherous, trustless, undependable, unprofessional, unreliable, unsure, untrustworthy

Antonyms: dependable, reliable, reputable, responsible, trustworthy