There's no victim here. This is how prediction markets should work. People who already placed their bids are completely unaffected by later traders. And if they choose to become a later trader because they were offered an attractive bid, there's an information exchange there. That's saying they have non‑public information that you don't have. Or they're bluffing that they do. You're not forced to trade with them, and if you do, then you are accepting that they might win the whole pot and be telling the truth. Trading with them is calling their bluff.