Paying enough people to troll enough web forums for there to be a non-trivial possibility the OP was interacting with several of them without being rumbled doesn't really seem orders of magnitude more difficult than paying a couple of "weapons experts" to lie for you, or getting some material your military possesses into a territory your military controls.
They tried that mate. But it turns out it's hard to find credible weapons experts that are total hacks with no qualms about lying. When it became clear that their chosen expert was going to expose the fact that there were indeed NO WMD's, he promptly died shortly before his report was due to be published:
https://en.wikipedia.org/wiki/David_Kelly_(weapons_expert)
By comparison, posting on online forums can be done very easily by anyone of any character.