Don't do it! Compare a new inexpensive one with the price of the refurbished one.
If it's only a hundred bucks or so different buy new.(it's all about warranty)
Your battery, hard drive, screen, keyboard have all been used and who knows if they have been abused. The warranty on a new Hard drive is 3 years.(it's because they only last about that long)
If it's such a deal you can't pass it up then: Make sure there are no stickey keys, not too many dead pixels, and the battery will fully charge and lasts several hours.
Typically they may load a new operating system as well so make sure you have enough ram so that its not too slow.