Back about 12 years ago I was the congregation secretary and decided to have a clear out of some of the old books in our congregation library and some we had inherited from the death of an elderly long time JW in our congregation - I just sold them on Ebay & donated the funds to the congregation. We made about £400 GBP , mainly because the books were in absolutely pristine condition in the most part.
When you actually sit down & read these books - you realise that they are total and utter drivel - the rantings of a delusional man , such as Rutherford or Fred Franz. The Society quotes them very , very selectively ( as ever , look for the .... in their quotations ) - no wonder they aren't available on JW Org.
Really old stuff going back to Russell's time ( like Studies in the Scriptures ) in good condition sells for big bucks. There are some avid collectors , especially in the USA - mostly with Bible Student connections.