It's quite hard to determine whether a second-hand monitor is good to buy or not. But you can consider these points.
Well, you need to check the brightness and contrast. Try adjusting them.
If the display screen is not in very good condition you will know just like adjusting on your TV.
Don't forget to check the sharpness of the characters and pictures displayed on the screen (desktop).
Check the physical condition of the monitor including cable. Don't buy it if the cable is not in a very good condition.
Also check the maximum screen resolution, by right clicking on the desktop, choose properties, then select Settings. You will see the resolution. Make sure that the maximum resolution is not lower than 1024 x 768.
Don't forget to check for BURN-IN on your monitor by displaying a completely dark screen. You can use Microsoft Paint, and fill the canvas with black color, then click the menu View - View Bitmap (or Ctrl + F). Make sure that you see completely black screen. If you see a red dot somewhere in the dark screen, that is the BURN-IN.
