Or the user can just post "ALL BIDS BELOW THIS POST ARE INELIGIBLE" at their desired ending time and that's the end of it. So they can just consider everyone's bids before that post, regardless of sniping. It'll be up to the user if they're gonna be jerks and consider higher bids below the post. Then everyone can just report their butt and hope no one ever bids for anything of theirs again.
Or the thread will automatically make such a post if the user is offline so that only bidders above the post can be considered. No one will scratch their heads because it's as simple as that. 8U