I built my first TrueNAS box using new old stock drives from eBay. Immediately after they arrived I learned SMART can be wiped, so I carefully inspected the drives for physical signs of use. Fingerprints, scuff marks, wear in the screw holes, insertion marks on the pins, that kind of stuff. They had none of those, fortunately, but the sealed anti-static bag had some weird half-English instructions that seemed extremely subpar for Western Digital.
So after careful inspection, all I could really guarantee was ... nothing. They appeared to be unused and the SMART was cleared. So far they've worked well.
But I just didn't sleep well trusting my data to them, so I purchased a set of new drives this week. These old drives are going into a tertiary local backup DAS where they'll be a last resort after my main external drive and cloud backups. They won't be a total loss, but I also won't be relying on them for anything.