From the site description... "The following list provides informations about old and special editions of the books by J.R.R. Tolkien and gives an overview of their worth. The prices are authentic market prices (for books in good condition). These books cannot be bought here.
The list is by no means complete but will grow continually. The prices of course are not guaranteed."

A few prices seem way off (for example the Ace paperbacks can be had for around $10 each in VG condition), but in general a reasonable list with nice thumbnails.