scratch A and you'll find B
scratch (something) and you'll find (something else)
If you investigate a certain type of person, organization, or thing closely, you will almost certainly find another, often contrary characterization or trait as well. There is a misbelief in popular culture that if you scratch a devout Catholic, you'll find a radical fundamentalist. My father always told me, "Scratch a successful business, and you'll find a hive of corruption."
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
scratch ˌA and you’ll find ˈB
(used to speak about particular types of people in general) carefully consider or examine somebody/something and you will find that they are different from their outside appearance: Scratch a senator from Texas and you’ll find a cowboy.Farlex Partner Idioms Dictionary © Farlex 2017