Can a cop be in plain clothes when they're radaring you on the road?

Q: "If a cop is clocking speeders with a radar gun, are they allowed to be in plain clothes, then have another cop go pull you over?" A: "In other words, what you want to know is if we can 'trick you' and catch you speeding. Well, it's not tricking you. Yes we can. It's not uncommon to see officers do that. At times, I as a traffic officer, have worked where it would be myself or another person in plain clothes. That officer will be working radar, and radioing to the other officers in cars nearby, who the speeder is.  So yeah, there's no get out of jail free card or no ticket because someone else was working the radar, not the person who stopped you." -- King County Sgt. Cindi West