Which is harder: pretending to be what you are, or to pretending to be what you are not? For example, imagine you are a news reporter, and want to, via your style and manners, convince typical folks that you are a) a reporter, or b) a stuntman. Which task would be easier? Which task would be easier for the stuntman? We could ask such questions about not just reporters and stuntmen, but about a wide range of other roles.
The way to convince the public that you are an X is to act the way the public thinks that X folks act. And the more vivid an image X folks have in the public mind, and the fewer real X the public know in person, the more the way X folks are will diverge from how the public thinks they are. And so the more work it would be for X folks to convince the public, via their manner and style, that they are in fact X.
So while it is probably easier for a shoe salesman to convince folks that they sell shoes than that they are a private investigator, I'm guessing that it is harder for a P.I. to convince folks they are a P.I. than that they sell shoes.