The bad ones have defects and failure modes of the follow:
1. Bad pixels - usually pixel stays black or fails to get past dark gray
2. Buzzing Coil whine, some much louder than others
3. Backlight white is not always the same "white" and it differs from monitor to monitor, and changing the brightness setting does NOT equalize them. Some "white" looks more yellow than others, the variation is too wide for something that should be consistently manufactured.
4. Deep sleep failure mode 1: refuse to wake up
6. Deep sleep failure mode 2: refuse to go into deep sleep mode even with the setting enabled and sits and vampires 12 watts of power while supposedly in "off" state, screen is black.
5. Bezel plastic has rough cut unpolished edges but not always at the same spots.