Loss is different in every legal system. Here in the US if market value of something is $5000 and your payed $5000 and it sell at auction for $2000 one could mark it as a $3000 loss. So all one has to do is make a stealth account buy the item for $5000, and sell it for $2000
So basically you buy something for $1000, list and buy it for $5000 on a stealth account, then sell it for $2000. Making $1000 and a filing a $3000 loss on your taxes.
Or that's my knowledge of the scam.
Edit:
Another opposite scam is when a buyer that makes a lot of fraud listing for and item at far less them fair market value to get real sellers to lower the price of an item they want to buy.
So basically you want to buy X but can afford it, so you make 100+ listing for X at 50% less then its worth, other sellers may lower there price to remain competitive allowing you to buy the item for less then fair market value.
I been around eBay too long. 😐