smack of evil; whiff of wrongdoing
Used when something seems dishonest, corrupt, or morally questionable; often implies a suspicion rather than proven guilt.
There's a whiff of wrongdoing in that politician's actions.
I sense something fishy about this deal.
A fixed phrase combining 不正 (injustice, wrongdoing) and 臭い (smell), literally 'the smell of wrongdoing'. The figurative use of 臭い for suspicion is common in Japanese.