Well, she may have made an "honest mistake." Or she may not. We can debate whether she should lose $600 or the author should lose the tickets, but that debate can only happen if the author made a decent attempt to prevent the loss, for example by offering the tickets second chance to other bidders or by driving down to the game and trying to sell the tickets for cash. He then could have pursued her for the difference between the $600 she promised to pay and whatever he managed to obtain for them using reasonable means to sell the tickets.

However, the author took it upon himself to defraud her out of the $600. He changed the situation from getting her to pay for the tickets she bought for herself into getting her to attempt to make money from arbitrage based on a false and fraudulent promise of his.

This is absolutely wrong, and it makes no difference whether she had originally backed out of the transaction or not. The story sets her up as a "bad woman" to play upon some of the most vile behaviours social animals have, namely believing that there are two classes of people, "good" and "bad," and the bad people don't deserve any decency or protection under the law.

I see defrauding her into paying for the tickets exactly the same way that I see bullying visible minorities or depriving persons we think are guilty of a crime of their legal rights. It stems from the same "They're a bad person, they don't deserve consideration" beliefs.

It may seem like a horrible Godwin-esque comparison, but how is this different from torturing a petty thief into making a confession? I don't mean to suggest that this is bad because "They might be innocent," I mean even if they're actually guilty, don't we as a society still want to treat them with decency?

This woman may have acted badly. But we should still treat her with decency, lest we as a society become vile ourselves.

In my judgment, both parties should be investigated by eBay. I don't know her side of the story, so I can't say what eBay ought to do about the choice she made initially. But if the author acted as described here, I would expect eBay to condemn his choice.