no flies on somebody
no flies on (one)
(there are) no flies on somebody
(informal)1 somebody is not stupid and therefore cannot be tricked or deceived easily: You can’t just tell her that you’ve lost the money; she’ll never believe you. There are no flies on Jane, you know.
2 somebody is skilful or clever at doing something: There are no flies on Jim. He can persuade anybody to buy a car from him.