About how many Marines took part in the Battles in Fallujah?

I am just wanting a fairly accurate estimate. I keep seeing a lot of people on different comment boards claiming to be Marines. After claiming to be Marines a lot claim to have fought in the Battle of Fallujah. I've seen so many I'm starting to expect some (not all) are faking this claim unless of course it was a major battle with 1000s of Marines. Kind of like how more people are claiming to be Navy SEALS than actually have ever existed. How do you spot a faker?