To be honest Ebay doesnt have any real resposibility or capilbility to verify if any product sold by a seller is counterfeit, fake or grey market, thats the responsibilty of the seller, as would be if a store in a mall was selling fake nike's, the mall is just the landlord providing a space for the seller at a cost to sell thier product in a place easy for buyers to come to.
They also are NOT in anyway beholden to the buyer to go after sellers that do any of the above.
They ARE however beholden to the manufactuer of the product being faked etc in that case the best deal to do would be contact the true manufactuer and give them the details of the seller and the product recieved and provide a link to the item that was fraudulent you purchased, then it will be up to manufactuer to ask ebay to have the seller to remove that specific good from thier listings.
Ive purchased many items from ebay, but it is a very caveat empour place, i know that going in and do alot a research before buying or bid on items that it wouldnt matter if there was an issue with, I bought an hp refurbished laser printer w/o toner carts for $10 US + shipping ($10 starting price no bids 1 hr to go), i figured even if it was just used or not refurbed by hp etc $10 + a small shipping fee wasnt much to lose, when i recieved it i called hp with the serial number, sure enough hp confirmed it had been refurbished by them. course it cost me another $142 for good carts from monoprice but still a $100 cheaper than anywhwere else for a brand new one and higher capacity carts to boot. that was 2 years ago and that printer is still running strong.