What you will find is that nobody attending the library book fairs has any intention of ordering books for their library(ies). They are there to get free stuff. Namely, as many free books as they can walk out of there with besides free food (if there is any). The stories told to each of the display services attending is that “They hope to be ordering books in two months as soon as the funding is approved for this quarter.” It’s not an actual lie. They will probably be ordering then. It will just be through the one big vendor they have always bought through and not a book being shown here has a prayer.
Every young or new author is wooed by the massive numbers of libraries. You spend money to get onto a library mailing lists and have 4 color fliers of your books sent out on those lists. The simple truth is, if your book isn’t being handled by one of those massive library sales machines it won’t be bought. Quite frankly you don’t even want it to be bought. Those vendors have locked into the library market by selling to them at half of wholesale. If you have a $90 book, the typical wholesale price is around $40.50 for your distributor and whatever they mark it up to retailers. The library is going to pay half of the $40.50 meaning $20.25. The vendor handling the sale will pocket at least half of that. In other words, you sold your book at or below printing costs so the vendor could make your printing costs and pay you at least 6 months after the sale.
The other dirty little secret about sales to libraries is they rarely, if ever, generate additional sales. You are always told to view the sale at a loss to a library as a marketing expense. In the technical book market, people check your book out of the library long enough to solve the problem they are working on, return it, and never think about owning their own copy.
If there is a particular library where people you know go to find books and you want to impress them, simply donate a copy of your work to the library. It will get put on the shelf and you will get whatever ego trip you get out of it. Selling books into the library market (especially technical books) is a business plan for living on the street.