If you were to buy a used laptop you should look the condition it was in. Like how good the screen looks and if it was damaged at all. Also, you should look at how good the disc drive is to see if it can run properly and if there are any liquid spills.
You should see how old the laptop is because if it’s older then 2 years the batter might be in bad condition or it might not have a built in wireless. It might also not have that big of a hard drive in it so you might have to replace it. To replace the battery and hard drive it would cost you around $180 to $210 so you might be better off getting a new laptop.