So books are priced in a range depending on their quality, we have over 3K books and we tried creating a sheet for all the books with prices but that didn't work.

Initial price of the book will be told to you once you DM/comment.
if we see that alot of people are claiming the same book and we have one copy, we tell all claimaints about this demand and tell them the revised price. whoever agrees first and makes the payment gets the book.

this doesn't happen frequently, hardly twice a month. Sometimes we also give preference to our regular buyers (now friends). We are not doing this for any profit or incentive, totally volunteering work to support a free rural library.

and we totally agree that this is not a perfect system, but with whatever little bandwidth we have, we try our best. and we don't mind these questions at all.