Cost/benefit equation
No retailer tries to eradicate ALL fraud, because beyond a certain point it costs more to do so than the fraud is costing. eBay probably feels this type of fraud is similar, given the small amounts the fraudsters are getting.
There's non-economic reputational damage from the people who don't get the goods they were sold and have to hassle with reporting it, but since eBay is making good that may end up being net zero (i.e. some people are put off by it, but others may have their opinion of eBay go UP because of how they were made whole)
If you had a convenience store where some high school kids would occasionally swipe a candy bar on the way home from school, costing $20/week, it is probably cheaper to let the kids steal as anything you do that would really prevent it costs more. Hiring part time security is probably the only way to prevent it, unless you set up security cameras over every single aisle. Even then someone has to watch them and take the time to fill out police reports and hope the cops don't laugh at them for reporting the theft of a 75 cent item!
Biting the hand that feeds IT
