The other way I often get books I want to read is via NetGalley and Edelweiss (to a lesser extent). Since I do book reviews here anyhow, those two sites are a nice resource for me as a reader.
Still, there are some books I will buy, and here are some reasons why I would do that:
- The book is a book I love. If I own it, it is likely I want to reread it again down the road someday. A book in this category is a favorite I feel I need to have on my book shelf.
- The book is by an author I love. Kind of same as above. If I really love an author, I really want to have all their works. However, recently I have relaxed this reason a bit. As great as some authors are, not all their books are that great. For instance, I like Stephen King, but not enough to own everything he has written. In the case of King, his books are easily available in a library anyhow, so I do not feel the need to have all his works on my shelf.
- It is a book or kind of book one my libraries does not have nor is likely to have. This is very applicable to various graphic novels, to most good manga, and to erotica titles among others. For manga I tend to like darker, more serious titles that are in contrast to the usual kid friendly fare most libraries have (if they have any manga at all), so I will buy those. That also applies for graphic novels. The same goes for erotica titles; few libraries are likely to have a decent collection in this area. Another area is Warhammer 40,000 books. Very few libraries I have found have a selection of these, so I tend to buy these. However, I am selective on which WH40K titles I get. If they are ones I know I will be likely to want to keep, I buy. If not, then I do ILL read them. The Horus Heresy series, part of that WH40K universe, I've borrowed so far via ILL. That series by now is at 30-plus books or so, and quality varies, so I borrow rather than buy.
- The book was dirt cheap, so I bought it. If I find a good book on a clearance pile, or at a library book sale, and it is seriously cheap, I may take a chance on it and buy it. If I like it, I keep it. If not, I pass it on. Same goes for the library friends book sale. Hey, for instance, one time I got the Real Academia edition of One Hundred Years of Solitude for a dollar. How could I pass that up? That kind of thing.
- The book may be in an area of study or interest, and I feel a need to have it for study. This is mostly applicable these days to Tarot, divination, and esoterica books. The library here does not really have these, and anyhow, there are a few I want to have in my personal collection anyhow. For some older titles that may be in public domain and such, I have found PDFs to load on my e-reader. For newer titles, I get the print if I can.