I only skimmed the article; I'd assumed that was part of the scam (forward the extra $100 on via western union, or paypal it back to me on this different account, etc)
The extra money is usually not a scam in itself if they are trying to actually get you to ship the item. Once upon a time scams were all about moving cash, but I surmise those have gotten harder, so now they secure your item and (presumably) resell it.
Thus, the promised extra money is actually just a way to both ensure you'll "sell" to them as they made the highest bid, and also perhaps an attempt at triggering just a touch greed which does wonders for putting the blinders on.
