Our company sold a fairly beefy server to a "customer" via eBay.
A little over a month later, the "customer" was complaining to eBay that the server was defective and not working right. Of course they refused our requests to call them up on the phone and troubleshoot the problem (and of course refused to provide logs).
They claimed the server kept shutting down.
So of course as all things go with eBay's habit of not usually caring about seller's side of the story, they demanded that we give them a refund and pay for the return shipping, so we are then stuck with quite a bit of costs involved in shipping said heavy large box both ways.
Get it in & look at the logs and every hour there is a entry saying OS requested shutdown.
Boot it up to the OS, remove their password so we can get in.
Discover they had a "evaluation" edition of Microsoft software installed that the "evaluation" period had expired and so every hour it was telling the system to shut down.
We sent them a strongly worded e-mail that if they can't "evaluate" products properly, don't blame the hardware.