I’m afraid I can’t help you with any eBay advice, but I am actually trying to collect
the Sierra hint books (although none with the invisible ink since I have
to able to read them).
I have most of the have most of the hint books, but am missing
King’s Quest 1 (both Sierra versions), King’s Quest 2, Leisure Suit
Larry 1 (only the remake), Police Quest 1 (only the remake), The Castle
of Dr Brain, The Black Cauldron, Heart of China, and all the Coktel hint
books except Inca 1 (i.e. I’m missing the 3 Goblins books, Woodruff and
the Schnibble, Inca 2, Lost in Time, and the Prophecy from Coktel).
The most prize find of all for me, however, would be the Space
Quest 1 hint book (only the original), as it doesn’t appear to be
available anywhere else.
In any case, I would be happy to buy the hint books or the games if you are willing to sell (directly or through eBay; it would up to you).