A few posts down in a different thread, we looked at what appears to be a forged Houdini 'signed' 1st ed. copy of MIRACLE MONGERS AND THEIR METHODS from 1920.   It's an old, ex-library copy that probably is worth about $150.  The dubious 'signature' ('authenticated' by GFA) elevates it to a $2500 asking price on ABE. 

I was reminded of a short blog entry that Houdini collector/biographer John Cox did on his site a few years back on forged Houdini autographs.  He specifically mentions the dangers on platforms like eBay and Live Auctioneers (which as also been recently discussed here on AL).

https://www.wildabouthoudini.com/2020/02/houdini-fakes-are-flooding...

Mr. Cox has other, more detailed entries about various specific Houdini forgeries throughout his archives. 

He also has discussions about real Houdini autographs that have appeared on the market (such as this postcard also signed by Theodore Roosevelt):

https://www.wildabouthoudini.com/2011/11/postcard-signed-by-houdini...

I highly recommend his blog if there is an interest in Houdini!