I buy direct from authors wherever possible. No problems so far. I don't trust reviewers (and definitely don't trust Amazon's review system). I maintain my own

I buy direct from authors wherever possible. No problems so far. I don't trust reviewers (and definitely don't trust Amazon's review system). I maintain my own library using Calibre. I have a directory on my laptop that has my books in it, and use Calibre to maintain and access it. I back it up onto an external hard drive about once a month. I briefly experimented with creating a Gitlab repo to store books in, so that it was at least as safe and secure as my code. But it's just easier with Calibre. Also I didn't feel entirely comfortable using Gitlab's free service for something other than what it is intended for, and I've learned the lesson that storing things long-term on free accounts isn't wise.