I sold and shipped the English QWERTY keyboard of my used laptop from North America to Eastern Europe.
This keyboard came with a computer I bought new and I myself and nobody else used this keyboard/laptop until I shipped it. I never spilled any liquid or powder on it. The keyboard has never given me problem and it is not from a bin of hundreds of other used keyboards. Alright it wasn't the best packaging in the world, but I did enclose it in foam and cardboard.
When it got there, my buyer told me that the 0 (zero), P, :, and ? keys are not functioning.
What troubleshooting steps can I tell my buyer? Or should I write this off at this point as a $20 loss?