I can't speak for John Reznikoff but RR Auction considers John Reznikoff to be an expert in authenticating documents and manuscripts of Presidents and leading figures of history.
We take authentication very seriously because we guarantee it on everything we auction forever, even though we don't own the items. I understand that he is a controversial figure to some who don't agree with his findings and those who question his credibility.
For over a decade, Reznikoff has been correct in his assessments for us 99% of the time. Our trust in him is proven because we sell over 12,000 authentic autographs every year.
RR Auction typically does not auction unsigned material so we have no experience in authenticating hair. I do know that provenance is very important and that hair of famous people was highly requested and collected in the 19th and into 20th century.
Reznikoff does tell his side of the story about the JFK/Marilyn forgeries mentioned
here on public radio, starts at about 26 minutes into the hour long show.