It would be a stupid to put into the public domain the best libraries to buy books from. They all seem to do it and I buy them all the time. They are always cheaper than second book shops and usually in good condition. I presume one of the reasons they get sold is that no-one ever borrows them.

And the other benefit is that they come ready classified. I got one today and the classification is clearly written on the spine of the book 914.212. This of course makes it much easier to know which shelf to put it on.