When my father died in 2001, I had no takers for his aircraft books. My father had been serving RAF in WWII and had a fair collection. I got a specialist in aviation books and he cherry picked a dozen, no more.
My mother died about five years ago and her books were more obscure and, again, charity shops not much interested as they were overflowing with books. I am now downsizing and expect problems in finding homes for the books I have not read in decades and won't read again. I want to deal with this, rather than leaving it to my family when I go West.
example: I have a top quality copy of Swift, Silent, Superb and contacted the owner of 'VCtenderness'. No takers. If anyone wants to buy - PM me!