What is not being said, or understood, is that Amazon doesn't actually sell anything. This is especially true for bicycle accessories.They facilitate the advertising, purchase, and delivery process for the very same retailers (and lots of others) that you know: Jenson USA, Modern Bike, Bicycle Outfitters, etc.) you could order a helmet directly from a retailer OR you could order if from the Amazon entity. If you look, you can see, and sometimes choose, which actual retailer you want to get the product from via a (possibly) local Amazon warehouse. You could potentially get a previously purchased and returned product in either scenario. As others have said, a used helmet, even slightly, should be easy to spot.

I can usually tell when/if the product I have gotten from Amazon was previously purchased. That really chaps my hide when it was sold as new. In some cases it is just not worth the hassle to return and re-order. If it was a helmet, of course, I would be evaluating the situation with safety in mind. For the last year or so, I have saved as much as 50% on some things that I buy on Amazon by actively choosing to buy products that have been returned after just one use ('like new'), refurbished and sometimes flat out, used. If I can save 50% off the price of a room fan or iPad, I'll definitely buy used. Shame went out of my game when I retired and went on a fixed income. Bed linen or underwear, I'll buy those new, thank you. I still have some dignity left. FWIW.