I recommend getting familiar with SMART and understanding what the various attributes mean and how they affect a drive’s performance and reliability. You may need to install smartmontools to interact with SMART, though some Linux distributions include this by default.

Some problems reported by SMART are not a big deal at low rates (like Soft Read Errors) but enterprise organizations will replace them anyway. Sometimes drives are simply replaced at a certain number of Power-On Hours, regardless of condition. Some problems are survivable if they’re static, like Uncorrectable Sector Count - every drive has some overhead of extra sectors for internal redundancy, so one bad sector isn’t a big deal , but if the number is increasing over time then you have a problem and should replace the drive immediately.

Also keep in mind, hard drives are consumables. Mirroring and failovers are a must if your data is important. New drives fail too. There’s nothing wrong with buying used if you’re comfortable with drive’s condition.