Not computer hardware, but the worst thing I ever got off a blind internet purchase was when I won an auction for an "As Is" Capcom Play System 2 (CPS2) arcade board for Marvel Vs Capcom 1.
CPS2 boards are 2 part boards contained in plastic chasis, and they're fairly large. Like, bigger than two-three keyboards stacked on each other.
Anyway, these boards have encryption on them and the keys to it are stored in battery backed SRAM. These are known as "suicide batteries".
The batteries are 1/2AA lithium cells, and have been running for 20+ years.
I think you can guess what happens when they get that old.
The board I had won was a spectacular mess. The battery had exploded, and coated a third of the board in acid. It was a horror show.
The moral of the story is to ALWAYS check your batteries, no matter what hardware it is!
I could only salvage 4 of 21 rom chips, the rest had most of their pins dissolved by the battery juices, and many of the SMD components were off the board entirely.