Be no/nobody’s fool
Definition 1 of 1
Pro Tip 1/3Usage Nuance
Used to acknowledge a person's wisdom in decisions, showing respect for their cleverness or skepticism. 
He may seem gullible, but he’s nobody’s fool when it comes to signing contracts.
Pro Tip 2/3Not Literal
This phrase is figurative and highlights someone's ability to avoid deception, not their actual foolishness. 
Don’t try to cheat her in the deal, she’s no fool.
Pro Tip 3/3Context Sensitive
Often used in situations where someone might be underestimated or taken advantage of. 
The quiet student surprised everyone with her insightful questions; she’s no fool.