the forum owners are in a particularly difficult position on BC as opposed to many other sites. BC charges fees to sell here. That means they benefit.
The BC owners would almost certainly be added as a Second Defendant in any civil court action. Seller as First Defendant, the forum owners being the second because they refused to police the sales, possibly refused to remove flagged posts (as per the post above) and earned some money from the listing.
Any claimant would be wise to spread the net wide, and the joint owners of BC are likely to have more assets to enforce against between them rather than 1 seller.
It doesn’t need FMIC to be upset, just 1 buyer.