I own several types of guns that the only way to decock is to pull the trigger. One does NOT pull the trigger to verify it's unloaded. To reiterate what others have already posted, you verify that the gun is unloaded by performing a press check, i.e. not only visually checking that the chamber is empty, but also sticking you finger into the empty chamber (especially when it's dark).
Anyway, when right before I press to decock, I'm doing my press check. I'm sure some who don't shoot much would think I have have OCD.. "hey.. why is that person doing a press check.. he already unloaded..". Oh well.. much better to be overly cautious before that trigger pull to decock.