ebay used to have people that did just that, westernsky, but sellers and dealers protested that their listings were being removed unfairly, that there was insufficient evidence, that the people who were accusing them of being forgeries were not qualified to do so, and some of the larger sellers who got caught "in the act" were threatening lawsuits and libel actions. In addition, the people who were working with
ebay were few in number, and given the arduous task of reviewing hundreds of thousands of listings. It was also rather thankless, since delisted items would simply be relisted, and deregistered accounts were soon reopened under new names. They would need 1,000 Bobby's for zapping the thousands of fakes that get posted daily, and that's just in Coins.
ebay profits from forgery sales: they receive their listing fee/FVF, and yet they are protected from liability by virtue of plausible deniability: "We didn't know the listed item was a forgery." Claims against
ebay by victims are onerous in the burden they place on the victim and minimal on the one placed on the seller: the victim must prove that the item is fake, instead of the seller being required to prove its authenticity. That does not make
ebay a willing partner, or imply that they condone sales of fake merchandise (they most definitely do not), merely that as a business there is no incentive to induce them to take some major actions against forgeries - they have low exposure to risk + there are very large costs to hire qualified employees in numismatic forgeries and counterfeits. When they see fakes, they delist them and NARU the offenders if needed, but it's a handful of little boys and their fingers vs. a Great Wall of China-sized dike that looks like Swiss cheese.
You might think that not buying raw coins is a good start, but the quality of the fake slabs is increasing as much as the quality of the fake coins, which is why NGC and PCGS and others are in a neverending battle, much like currency designers, to make their product tamper-resistant and discourage counterfeiting.
In the meantime, if you suspect a fake, report it, please. Crowdsourcing is the only real way of getting the number of "eyes" needed to scan those hundreds of thousands of listings and report the questionable ones.