I have written about the whole "Cast Signed Movie Posters" scams in the past. IMHO 99% of the "cast signed movie posters" on eBay are forgeries. Many have created bogus "COAs" that are supposedly directly from the studios, (Universal, Disney, etc) and they are simply bogus pieces of paper.
You have to be extremely careful buying any "cast signed" poster, and realize that it is almost ALWAYS fake... and usually in the same hand. Often they'll switch up the marker colors to give the "appearance" of being signed by multiple people, when it is still not the case...
Look at the photo on this one, even the logo is cut off. It's a poor kitchen table job. And why you would have Tom Felton's signature on a photo he isn't in is weird, also Rowling on HP stuff other than books is super rare and very expensive.