I think the main thing that screws up is the bearing the thing spins on. Sorta primitive but if you have the hard drive running outside of the computer and hold it up to your ear you can listen to it. I've lots of hard drives that Disk Utility says are fine fail.
Hard drives run at such a high RPM it's a wonder that they last as long as they do. Like probably most people on this site,I have a box of old hard drives. Some dinosaurs like 4 GB units. I wouldn't trust any of those suckers. I'd wipe them and instal an os and use them for sure, but whenever I work I save every few minutes and every few hours copy the last saved version to a flash drive and second hard drive. I try and save lots and lots of versions on a multitude of hard drives. I wouldn't trust any used, or even new hard drive all that much, I'd plan on them failing. I trust flash drives way more because they don't spin.