I had heard the same thing from one of my regular vendors. The law allows for private sale of firearms in Oklahoma. The ATF is cracking down on some folks that are buying and selling used firearms as a business without a having a FFL.
There's some of them out there, they hide behind the hobbyist status though and go prove it which really does hurt us all in the end.
I won't buy from an individual if I think that may be going on.