Based on my experiences with non-recognized tribes of other affiliations, I'd be willing to best that a lot of those "fraudulent" groups are legitimate Native American tribes, or at the very least organized groups of people with shared Native American ancestry, but ones that are not officially recognized by the US Government.

Yes, there are fake tribes that come out of the woodwork hoping to gain casino rights, but many if not most of these non-recognized groups often accused of being fraudulent have verifiable histories going back 100 or more years, and have been studied by historians and anthropologists (with publications to prove it). It's a shame that such groups are denied the recognition they deserve, even after all that has happened in this country.