I've been going to 7 Days a Week Smog for years. On my most recent smog check, I hadn't noticed that the engine light was on. They told they'd wait on the Groupon and to just bring it back when the problem was gone and the error codes reset and ready. Very civilized.
I will say that they used to have better snacks in the waiting room—but it's amazing that they even have a waiting room, let alone snacks.