All you can do is try with eBay, check the seller's feedback reputation - you will soon pick up on whether or not they are good sellers and other buyers are pleased. Why not test by boying one or two, if you are pleased then you can go back for more. EBay does have a few rogues but the company is working very hard to keep the site safe. If it says "genuine Brita cartridges" then that's what they must be, if not you can send them back and have your money refunded. Good luck!