How do you feel libraries affect book sales? Are they generally a positive force (ie. they buy more books than otherwise would be sold) or a negative force (the # of readers who would have otherwise bought a book and get it from the library instead outweighs the number of books sold to libraries)?

This is an interesting question. And like many sales questions... It depends.
But let me expand on that a bit.
When I first started at Vertical, I thought expanding the library market would be a great idea. We would add a new channel. One that restocks if books are lost/damaged or if lending numbers are high. There are many libraries across the country so they can fill in for the drop in chain stores.
Well, it isn't a bad idea. But it is also a tough sell depending on what you publish. Vertical's catalog isn't really youth focused. We have a lot of 16+ and 18+ content. And while programs like YALSA have selected some of our books in the past, even such programs haven't really moved the needle much.
I kinda feel that libraries are good indicators for what the masses want. And not so much the best place for the middle or the fringes of reading (unless you happen to have a huge library/library system in your area).
So while books like Twin Spica, Tezuka titles, Chi, and the Shinkai books...the rest are maybe sampled or often ignored.
Libraries were at one point up to 18-20% of our sales back in 2010. We even went to ALA from 2010 to 2011. Now I think that's down to around 3-5%. Meanwhile store sales and online sales are going up for us. Go figure.
So it isn't something we ignore, cause our distributor has a devoted library sales department. But it is also something we do not always go after with every title we release.
On the novels side that's a different story. And library sales are much more significant there. We do better in the academic libraries world though.

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