Yellowing screens, slopped on thermal grease, warped screws, etc...
mymacbookpro2011 and ifixit and other sites have shown the quality put into the Macs is not there. Even the 2009 iMac I sold, the purchaser contacted me a couple years later to report the screen had yellowed with burn marks due to heat and was thankful I bought the extended warranty... given that issue was a widespread issue, Apple is selling the IMAGE of quality. Plenty of websites, like those I'd mentioned, go into plenty of detail.