I would never buy something so delicate second hand from a private seller, full stop.
I've bought motherboards (3), hard disks (5), memory (10), CPUs (6), sound cards (3) and several graphics cards 2nd hand, and I've only had a couple of problems, with a graphics card and a sound card. That "failure rate" is not dissimilar to what I've seen on new HP server kit over the last few years.
Over the last 20+ years, I've found most computer components to be quite robust and surprisingly resistant to careless handling (not by me of course
).
I've seen lots of failures of PC components "in action" but none that I can remember through poor handling.
That's not saying it never happens, just that it is perhaps less of a problem than it may be made out to be.
SD