Thing to check on used DSLR?

Hi guys! I'm planning to get a 2nd body as my back-up. And I want to get a used DSLR than buying a brand new. I'm just wondering what are the thing to check when buying aside from the cosmetics? How will I check if all the pixels are working, how to check the shutter count and etc? Thanks!

P.S. @ Moderator, I'm not sure if this is the right thread for this, if it's not, kindly move this to the right place. Thanks!

There is a free program called Deadpixel test. You take a pix with the lens cap on and it will tell you about any hot or dead pixels. Take some pix with the camera at different shutter speeds, aperatures in different modes. Look over the results. Shutter count - you may not be able to determine it. Depends on which camera you get.

If you have access to the body you may want to bring a focus chart and do a quick front/back focus test.

Thanks guys, I'll do your advice.