Terry Pratchett has written how many books? A bazillion? Two bazillion?
The largest used bookstore in the region (McKay's) had exactly two, count 'em - two, Pratchett paperbacks in the shop: Guards! Guards! and Going Postal. There are damn few authors anywhere near that prolific that are that sparsely represented in the used book stacks (*coughHeinleincough*)
(PS: It was weird; today was the first time I ever carried books into a used book store. Whoever gets the copy of the 2nd edition of the Standard Catalog of Smith & Wesson that says "TAM" in Sharpie inside the front cover, use it in good health...)
(PPS: FireFox's integral spellchecker recognizes "bazillion" as a word. But not "spellchecker".)