Still, my household(multigenerational) has too many books, and this is mostly an artifact of a childhood that gave me plenty to read. We even still have the incomplete Funk & Wagnalls encyclopedia picked up from when the school library dumped them.
It'll be the "great book downsizing", for us. Someday. Occasionally I look into scanning the ones I have sentimental value towards, and there are services to do so...but really, that would just displace the problem into "digital junk hoarding". It's hard to let go of things, especially in the gradual way that fits with our waste stream system.
The best tactic I've had to deal with it is to first make an explicit division of space (no piles allowed, at least have a tray or tie the bundle) and then use the divisions to create a ranking mechanism. You don't have to let go of things immediately, but whenever you have a day where you value space over stuff, the low rank stuff can be taken out with minimal ceremony: "thank you very much".
>Listing and selling on eBay
Yeah, unless something is a big ticket item, eBay isn't worth the effort. You used to be able to outsource it to someone for a cut but nothing like that seems to exist any longer.
[1] https://londonist.com/london/books-and-poetry/bookswap_eastc...
I mostly just end up throwing them away a few at a time.