be no fool

be no fool

To be worldly and difficult to trick or deceive. Your teacher is no fool—she'll never believe that your homework blew away on your walk home from school.
See also: fool, no
Farlex Dictionary of Idioms.

be no (or nobody's) fool

be a shrewd or prudent person.
See also: fool, no
Farlex Partner Idioms Dictionary

be ˌno/ˌnobody’s ˈfool

be a clever person who cannot easily be tricked or cheated by anyone: You won’t be able to cheat her — she’s nobody’s fool. Don’t underestimate him. He’s no fool.
See also: fool, no
Farlex Partner Idioms Dictionary
See also:
  • be no/nobody's fool
  • deceive (someone) into (something)
  • deceive into
  • diddle (someone) out of (something)
  • diddle out of
  • diddle something out of someone
  • con (someone) into (something)
  • con into
  • pull the wool over eyes
  • pull the wool over somebody's eyes