An interesting question/claim/whatnot. I'll address it in parts - starting with things which are false to the best of my knowledge, and moving on to parts which are true or likely true.
I should start by saying that the name Henry Ossipoff Wolfson is a complete unknown to the documented history of the Flat Earth Movement. There is no record of any person by that name having been in the Zetetic Society. This claim of an exposé appears to originate from a
New Yorker article, and is made with no reference to a source. Some of the wording in the supposed exposé is very similar to Christine Garwood's phrasing from
Flat Earth: The History of an Infamous Idea (which I recommend - it's rather unfavourable towards FET, but the research into the movement's history is of a high standard). I have a sneaking suspicion that Mr Wolfson's words (or even existence) may have been at least partly fabricated.
As for his travelling salesman routine, there's a nugget of truth to that. It was widely alleged during his life that he was a quack going by "Dr. Birley, PhD" (of
Birley's Phosphorus fame), and that he sold and various products claiming to improve one's health. Did they have the curative properties he was promising? Almost certainly not. It's hard to say with certainty whether our Rowbotham and "Dr. Birley, PhD" were the same person, but given that Samuel Rowbotham filed multiple patents, including one for a "life-preserving cylindrical railway carriage", I'd say it's at least believable.
That said, Rowbotham was many things. He was also a travelling socialist lecturer advocating for a regime change, for example. I wouldn't rush to conclusions about his Flat Earth belief being disingenuous. He was far from a perfect man, and I'm willing to believe that he did swindle people towards the end of his life, but it would be unfair to say that his entire life was a lie.