One of the most profitable ways of finding inventory is going to a library book sale that is NOT advertised on BookSaleFinder.com. The reason is simple – you will most likely be the only one there with a scanner (i.e. buying for resale purposes). So you will get all the profitable inventory for yourself.
My biggest score at an unadvertised book sale was on a Friday afternoon in a suburb of Chicago. The library was culling their inventory and selling their books for a $1 a bag. I knew this was going to be a good day because I was finding many ex-library books worth $50+ and a few worth over $100. I walked out about 3 hours later with 16 bags and a total investment of $16. When I got home, I re-scanned the books and the total Amazon value was $4000! Needless to say, I was the only one at that sale with a scanner.
There are a couple ways to find unadvertised book sales. The first way is to do your own research.
1) Do a Google search of every library within 2 hours of your house.
2) Call (or email) them and ask when their next annual or semi annual library sale is.
3) Check BookSaleFinder.com and see if that sale is listed on there.
4) If it is not – then you have a winner. Write down the date and location on a big desk calendar.
For another possible angle, try using the website Book Sales Found. They contact every possible book sale source in the country including libraries, hospitals, and universities. Many times these sales are not advertised on any other website. It's currently $10 a month with a 7 day free trial.
I work at a mid-sized public library and we have a book cart by the entrance that we load up with items that people have donated. Since I’m the one who goes through the donations, I can tell you that people donate a lot of valuable books! We also have a Friends of the Library bookstore in one of our larger branches.