no flies on somebody

no flies on (one)

One is very active or works at a fast past. Alludes to the idea that flies do not or cannot settle on fast-moving animals. There are certainly no flies on Judy. She works so fast that the rest of her team can't keep up with her.
See also: flies, no, on

(there are) no flies on somebody

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.
See also: flies, no, on, somebody