Forgeries are regularly offered on eBay. Last summer the publication of the fifth Harry Potter book drew much interest and the number of "signed copies" of J. K. Rowling's books offered on eBay soared. The amount of obvious forgeries bought by unsuspecting fans astounded James Allen, owner of Red Snapper Books, a rare book dealer. "Of the fifty or sixty items you expected to see at any one time, perhaps two or three were genuine," he said.

Seeing people spending hundreds of pounds on fakes, Mr Allen wrote to buyers and sellers. "You can imagine the sort of replies I received from the vendors," he said. "But many buyers thought that I was competing to buy a defaced book, they were so eager to own a signed Potter."

Harry Potter fans would do well to be cautious. "There's no magic about this. A signed Harry Potter first edition offered on eBay for Pounds 30 is not likely to be authentic", said Neil Blair, a lawyer at Christopher Little, J.K. Rowling's press agent.

Be aware that certificates of authenticity are often worthless. It may be wise to go to a reputable dealer to check. Also insist on digital pictures of items and ask questions until you are satisfied.