I am planning a set piece that involves some NPCs deceiving my players. The short version is that my players will meet some simple farmers trying to bring their crops to market, only to find that they're actually smugglers in a Hatfields and McCoy's type feud, which the party then gets messily swept up into. I generally don't trick my players; I don't think there's anything wrong with it but I imagine some tables would take to it more than others. Do you trick your players? Are there some tricks you find acceptable and others that are unacceptable? For me, I have no qualm getting my players swept up into the seedy underworld of drug or artifacts smuggling, but I don't think I would run a plotline on human trafficking. That I think would be difficult in an unpleasant way for everyone involved.