Harry Potter isn't my area, but if you put it on eBay you could risk losing a lot of money if you don't know what reserve to set. Personally I would sit on it till there's a specialist book sale at an auctioneers in your area and then ask the auctioneer (as he gets commission he has a vested interest in getting you the best possible price). Hope you get the price you want. A slightly cynical ploy, as an afterthought (I'm in the antiques trade), is taking it to a secondhand book dealer and seeing what he offers you for it - dealers normally offer you about a third of what they can sell it for. Good luck!