Side-by-side, double barrel shotguns are usually easy to tell apart:
You have boxlocks….

And you have sidelocks…

But sometimes it’s not so easy, like with this Bernardelli:

It sure looks like a sidelock, right? It has a sideplate, there are pins in the sideplate, a tumbler axis for the hammer (tumbler). But those sideplates are very misleading. This Bernardelli is actually a boxlock. And in this pictures you can see the sign that gives it away:

See the screw to the right of the barrel lump (the square, blued piece in the floor of the action)? That screw holds a plate in place. That plate comes off so you can access the gun’s locks. The locks are are mounted on the action, not the sideplate, and the plate gives this Bernardelli’s true status away.
The sideplates are ornamental and designed to make this double look like an expensive sidelock, while the gun is really a boxlock, sold at a more affordable price.