I picked up a MacBook Air on Craigslist for $100 with a dead, swollen battery & horizontal + vertical lines on the screen. Replacing the battery somehow triggered slow, fluttery, goofy booting & a left shift key which doesn't work or uses ALL CAPS which can only be reset with a restart :-/ Upgrading the OS to macOS High Sierra did not help. After a few months, Apple updated macOS High Sierra, which fixed everything except the lines on the screen. I'm happy with this $100 MacBook Air now, lines on the screen included. I wish I only had 1 line on the screen :-)