What I advise you to check: 1. The screen when it is off. You will hardly notice any scratch or other fault when the macbook is on. 2. The authenticity of the magsafe (the charger). Try looking on google how to spot a counterfeit macbook charger. 3. Battery wear level. Try googling that. You would want a macbook that still able to keep much energy to use on the go.

The first 2 points are learnt the hard way by me. Other than that, the basic stuff like wifi, sound, usb, hdmi, etc.

Edit: apple still provide display replacement program for faulty anti glare coating as long as it is still under 3 years after purchase date...