I try to get used books over new almost always. The only exceptions are for books that just came out that I desperately need to devour instantly and the library physical/digital wait is months.

This is pretty much true for most things in my life, I look for used/freecycle first for anything I need for environmentalist reasons. I remember seeing a comment years ago about how even those who are anti-consumerist still have a huge blind spot when it comes to books, and that was totally me - I had dozens of books I’d bought before ever reading, only read once, and didn’t even like that much. Having to declutter all of those books for a move was exhausting - used bookstores wouldn’t even take most of them for free, regardless of condition or how much I’d originally paid for them - and I’ve been trying to only purchase books I’ve already read, know I’ll reread, and that I can find used in good condition.