eBay actually does quite a lot to combat the sale of counterfeit items here.
eBay enables brand owners to report any listing that they consider to be counterfeit, when eBay will remove it. (In fact, we receive endless questions from sellers about items they claim were removed unfairly.) For details, see VeRO at the foot of the page.
But the nature of eBay means that there will always be scams and scammers here. eBay even warns buyers in the user agreement that "they do not guarantee the existence, quality, safety or legality of items advertised, or the truth or accuracy of descriptions".
Buyers can't say they were not warned. eBay isn't like the shops. eBay is a jungle.