They'd basically have to lie stupidly and get caught in it before you could catch them. (Or fail to lie about something that they should have - like a wanted criminal on their crew)
Vs a military grade inertial compensator and say a ship with a "tuner problem" headed towards a grav-wave? Honor/Fearless CL-56 are already in possession of a communication showing that Haven was up to it's elbows in the "native insurrection", and the interrogate by comms question is simply a pretext to "play cop" and say "pull over to the side of the road, Capt. Coglin".
If it wasn't a Q-ship, then even that would have stopped a communique after Sirius reached the hyperspace limit and went off to the Havenite task force. A more interesting bit is that Coglin was planning on telling that task force to stand down because Honor's marines and pinnaces had prevented any pretext for seizing the planet and terminus to begin with, which is WAY less fun for us as readers than that first death ride, and worse yet doesn't put Honor in the Heavy Cruiser version of Fearless in HotQ.