This is too broad a subject. Art History, Photo History, contemporary images, equipment manuals, film processing and printing guides, alternative process guides and monographs?
I have about 10 lineal bookshelf feet of photo related books at the moment, as well as another 3' of a 1965 photgraphic encyclopedia set. I just feel I am scratching the surface with this many at times.
There is a guy in the Toronto are who buys up estates of jewellery, precious metals, militaria, and photo gear who then flips a lot to sell online.
oI saw an ad in the local Craigslist that he has a garage full of photo boks that he wants to shift for $500 obo. I am resisting it.