How does a parent check that a friend isn’t passing pills to them in the back of the bus? How are they checking that they don’t shoplift when out on their own? This is not an argument.

Do your best as a parent and that is enough. Perfection is not possible or even desired; kids do have a degree of agency, and if they want to break the rules they are going to do it! And breaking some rules (ideally in a safe-ish way) is one way that we learn how to be independent from parents as we mature.