No ability to enforce makes it moot. At most you get banned from the forum.
I imagine its like ratings on ebay but much much higher stakes.
As you mention, eBay for the longest time was one of the only/biggest way to sell things online, and reputation on there could make or break how successful your business would be. Similarly, if this forum is used by the majority of people doing business on the dark web, then obviously it isn't "moot" as not following the decision is equal to heavily handicapping your business..
On the other hand, if the group accused is large enough, like some of the $20M ones mentioned in the thread, I assume said groups could easily spin off their own community or still have business even if they were banned from this forum.
Of course, it's a different topic if the decision was against them for clearly unfair reasons.
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=586941
This is like a buy-one-get-one-free comment, not only is the above about evolved dispute resolution systems, it mention the moot.