Here's how to handle fakes.
It should also be noted that Fournier was one of the more famous forgers. Another was Sperati. Some of their forgeries have become a bit collectible since they make an excellent item for comparison and are usually cheaper than the originals.
From this page
http://bigblue1840-1940.blogspot.com...Forgeries.html
Another thing to note to save you having to read the whole page, for that stamp there are originals, reprints done by the printer, and forgeries made to fool collectors. (The article is a bit interesting, and shows more forgeries than that one with explanations.)
Steve B