Yes, it's suspicious and I have questions. But it's also plausible that it's all legit.

People who donate books often overestimate what their books are worth. Selling the books and using the money to fund the library (which can buy books it actually wants) might be more efficient than paid staff handling a bunch of books they mostly don't want. What's the expense on doing the work themselves, and can outsourcing beat that?

Also, it seems like people who donate stuff have lots of other illusions about how much good they're really doing, and the people actually doing the work will entertain those illusions, but they have to deal with reality. Personally, I'm fine with anyone who takes stuff I don't want off my hands for free with no hassle.