The assembly, before you even power it on
The first instinct is to pick the screen up. You look at whether the hinges are properly fitted, whether the gasket sits correctly, whether the housing has been properly re-anodised, and whether all the flex cables and connectors are in good condition. The gasket should be smooth, even, and slightly higher than the bezel to protect the panel. The polariser should be perfectly bonded, without a single bubble or lifted area. Careless assembly here means a screen that comes back to you as a warranty return.
The 10 second check: raking light across the edges — an even gasket, a well-aligned bezel, no flex cable poking out or pinched under the frame.