Re the ethics of being a narc or a snitch.
Most of us outgrew this schoolground mentality of "thou shalt not tell teacher". Bottom line, if I believe my next door neighbour is selling drugs, I would become a narc. Same if they are cheating the IRS. I would snitch.
I have "turned in" in my past a number of airline staff for selling their travel benefits, and would do the same again. I didn't entrap them, but was a station manager at the time and it was pretty easy to spot. Why? Because it is defrauding the company, and as such no different from taking cash directly from the till. (the passengers who bought the passes were business flyers, who would otherwise have bought revenue tickets)