On eBay, make sure you run the seller's ID on ToolHaus so you can read all the negative/neutral reviews to see if anyone's questioned the authenticity. Also, as far as online retailers in general, stick with the names mentioned on this board and run a search to find threads on particular retailers. You'll be fine. Also, make sure that retailer has a good return policy. It's best if you familiarize yourself with a scent by smelling it at a store and trying it on yourself. Your nose is pretty much the only way now to tell if something's fake.