I bought a used Macbook. It worked great for 2 months, then the screen got some vertical lines that didn't go away. It happened while I was using the laptop and I thought it was a software glitch but nothing I tried or googled fixed it. I submitted a warranty claim and sent it in. 2 weeks later I get the laptop back unfixed because they said I had put "pressure" on the screen and it is not covered under warranty. I figured it was a pre-existing defect and somehow it got triggered while using the laptop. Now I'm out about $250. You never know if you are buying a lemon when you buy a used laptop.