The Illustrated Guide to Criminal Law
Chapter 12: I Was Entrapped!
Entrapment pg 22: Undercover Police Committing Crimes
(There are limits on what crimes undercovers can engage in. They can’t hurt someone, for example, or conduct illegal wiretaps or otherwise violate their targets’ constitutional rights.
But they are allowed to commit crimes incidental to their undercover role. So a cop posing as an addict is allowed to buy and possess drugs. And Saul was allowed to do so in his role as dealer.)