The one thing I was not thrilled about, which I do not see so much anymore, were the posts by people who said they refuse to trade with/sell to/buy from non-members.

Can't do much about that anyway. Sellers who are members or non-members are free to deal with whoever they choose, pretty much like ebay sellers blocking bidders.
I have received a couple of 'complaints' as such in the past. I can only respond "Sorry, not my problem, sort it out between yourselves"