From the way I've seen it. When a thread is started by a HOS member the mods have allowed a single post (not a pile-on) informing the seller, and potential buyers of his status.
Also there is nothing stopping people from PMing people who have bought in the thread and sending them a link to the HOS status. If they weren't aware of that fact before purchasing it has been grounds for canceling the purchase without PL repercussions in the past.
I am not sure if any of that has changed, given the mods new threadcrapping extinction agenda, but that's how it's worked in the past.
One post? Perhaps a sign might stand out more...
I can't wait to post these.