This old model had poor protection for the underlying logic board if liquid got into the keyboard. I once opened one up and found blue-green crystals all over the logic board, crystals that gave off a feral smell. Turned out the person's daughter (the user) had a pet ferret who liked to run across the keyboard... and she did not realize that ferrets pee as they run. It had sprinkled her keyboard over and over until the unit shorted out. That was just ... nasty. Pull the RAM chips, and check for corrosion on the connections – a sure sign of further liquid damage. Those old white MacBooks were a giant pain to work on for anything more than a drive swap, battery replacement, or RAM upgrade, and are worth less than a tank of gas these days. My Opinion: The repair isn't worth it. Pull the drive, save the data, and advise them to get something newer. Doesn't have to be new – not all of us have that money – but something within the last 6-8 years. Perhaps you even have such a used unit already that you could sell...

Retired Mac repair person – doesn't mean I know everything, but that I've done a whole lot of repairs and have seen things. Your display has layers, the glass being only the part closest to you. There's an interesting teardown of the retina display here on iFixit, and if you want to geek out, you are welcome to read it. My point is that things can happen other than cracked glass. If your computer were on my bench, I would: (1) With the computer off, run a credit card or similar thin plastic all over the screen, edge first, to see if I could locate a hairline crack that was otherwise invisible to the eye. If I did, I would feel a little "click" as I ran across it. I would not press hard, just enough to catch any edge. Then, if that did NOT produce any results, I would... (2) Boot up the computer, and carefully flip it upside down, holding it by the bottom case (keyboard part), with the screen towards me. Then I would shake the computer a bit, to see if the curved thing moves. Reason: If it's a loose wire...