In a recent judgement, the German High Court confirmed its ruling from 2004 about the liability of eBay in cases of repeated Trademark infringement by third parties.
Once eBay has learned about third parties abusing trademarks, it has to prevent the third party from repeating the infringement. If eBay fails to do so, it is liable.
The plaintiff in this case was Rolex, who found hundreds of cases of product piracy on eBay.