All bets are off these days in online sales of autographs. If it's not Stephen Koschal selling them, it may not even be a real COA from him. There's another item we've been looking at today on another thread with this problem.
I will play devil's advocate. In the recent past, I have purchased two items from Mr Koschal. Both were reasonably priced for what they were. Both also 100 percent authentic and unique in their contextual significance regarding the signers involved.
This is not an endorsement. There are also items on his website that I personally find questionable. This is just a response to your inquiry about having knowledge and experience with him.