You might want to check out Luis Rosmann's videos, a famous Apple repair geek who fixes for cheap the products Apple themselves misdiagnose[1] in order to rip off their customers[2].
[1] https://www.youtube.com/watch?v=V7RXJP4mxCc // teenager's MacBook's display is not working correctly so Geniuses tell him he needs a new motherboard replacement while Luis discovers in 2 seconds that the lid-close sensor cable is broken so he replaces it for $8
[2] https://www.youtube.com/watch?v=o2_SZ4tfLns // customer's MacBook's display is not working correctly so Geniuses tell him he needs a new motherboard and display replacement while Luis discovers in two minutes that the display connector has a bent pin and fixes it for free