This recently concluded sale on Ebay prompted a question on nature of the secondary or ``collectors'" market for old and out-of-print WT literature. Apparently, it's become a fairly well-established collecting speciality. As do collectors in the more established collectible sectors of, say, coins and postage stamps, one would imagine that in time the players would sort out issues relating to ``fair market values" of the various old books and other material, their relative rarity, etc., and that collectors guides, reference sources or price lists would begin to turn up.
Are any of you collectors of this stuff? If so, are there reference sources available?