Trust your eyes - the first things I look out for are the spokes of the wheels. Those watchmakers who spent a lot of time on hand-finishing tend to carve their spokes to an impressive 3D effect, for which you can see the anglage of each spoke from an overhead position. Then there are obvious signs like sharp interior angles which are time consuming for watchmakers to do. The curvature and depth of each anglage suggest the difficulty and the hours involved.
A short video of beautiful finished spokes.