- If you put your Macbook on a flat desk, does the aluminum on the bottom touch the desk? (The rubber feet should touch the desk; aluminum should not.)

- If you close the lid, does it seal all the way around? (You shouldn't need to apply pressure to make the lid seal. Closing the lid should not bend it. It should not pop open on its own.)

- Cracked trackpad is a bad sign

- Look along the edges; any warping is a bad sign too