I understand the implications of the 501c3 status.

But we should all know that the Club can sell whatever it wants as long as the profits go to the club. If someone wanted to
donate a car to the club and take the tax write-off... we can sell it and keep the profits.

The ANA has a blog, not a message board like the Club. Here is their Blog.
https://www.money.org/blog/tag/websitehowto
No one sells coins there as far as I can see.

I guess I have my answer, and I'm OK with it, thanks for your responses.
I'm gleaning that the Club wants to limit the Club Message Board to Club related stuff.

I still doubt that member to member sales on a club message board would violate the 501c3 rules but I'll drop it.
I'm not a lawyer and if there is a grey area there, I'll stay away.

Thanks again for the consideration.