One of the interesting things about people who act badly is that they have a tendency (well, it's a human tendency) to see things only from their own point of view... and in this perspective, there will be a superfluity of reasons why they aren't so bad, why their bad behaviour isn't so bad, but anyone who takes offence to their behaviour is - by so doing - worse.

For instance, a new buyer on eBay pops up, bids or buys, and fails to pay. Why? Oh, any of a myriad reasons. They didn't mean to bid. They didn't realise it was binding. They needed or wanted the item at the time of buying but a second later the whole world changed and they suddenly didn't need it. Their pet goat pressed the button. Their financial situation altered in a microsecond and suddenly they couldn't afford the item. On a final in-depth search in the bowels of the laundry cupboard they found the original item which they'd been trying to replace. They suddenly found it cheaper elsewhere. They wanted it for a moment but the want wore off as soon as they'd won it.

Whatever the reason, in his/her mind the new buyer will scarcely even acknowledge a smidgeon of fault. Perhaps the buyer would admit "Well, yes, strictly speaking I am supposed to pay but --" and the "but" comes. The "but" means "I am not really at fault." Whatever words make up the "but", it's a complete exoneration of the buyer.

So... when the seller suffers the inevitable consequences of a buyer who doesn't pay or finalise the transaction, and takes action in respect of those consequences, the new buyer is already primed to take affront at whatever the seller says or does if there's even a hint that the buyer is to blame.

Some people simply won't acknowledge fault, and will feel entitled to take umbrage if they are held to account. Best to just keep such people on the perimeter, and follow your policies (which you'll have set up beforehand) as appropriate to various situations that arise.

It's not that I don't believe human beings are capable of acknowledging when they're wrong, or learning from mistakes... but so much of modern life seems geared towards a sense of entitlement and an invisible thought helmet which keeps giving feedback loops of self-justification! On eBay, this sense of entitlement is part of the mantra heard by buyers, and it creates an artificial environment where sellers can easily feel herded into the cattle-trucks of Jawohl, Herr eBay.