How is attaching themselves to the page even possible? I don't believe Amazon has any kind of ad system which allow people to buy spaces.
For example: https://www.amazon.com/dp/B00KRYMB88/
The ASIN is B00KRYMB88.
Whoever FIRST listed to that item picked the title, description, pictures.. and it created the page on Amazon and assigned it an ASIN. If you have an identical shirt to that, you can list it with ASIN B00KRYMB88, and it will appear on that page (But you can't edit the listing details). That is how Amazon is built.
The problem is, what if you have a counterfeit shirt, and you sell under the same ASIN. A customer will get it delivered.. it sucks maybe.. and you blame the listing and leave a bad review.
Though given e-commerce is trying to replace traditional brick and mortar, they might put more effort in ensuring quality.
So its possible that you can "sell" an item that a different supplier actually sent to amazon.
In other words, if Seller X, Y, and Z all sell Widgets, Amazon puts all their Widgets into the same box. When you buy a Widget from Seller X, you may actually be getting a Widget that originated from Seller Y or Z. From the buyer and seller perspective, it's transparent...unless, of course, one of the sellers is a counterfeiter, in which case the buyer gets agitated that Seller X is selling counterfeit Widgets and yells at Seller X for selling counterfeit Widgets when the item actually originated with Seller Y.
Is this also true of items shipped and sold by Amazon.com? I avoid third party sellers for this reason.
If a product is not on Amazon, you create a listing, add images, descriptions, etc.
Then everyone that has the same product has to add their under your listing.
That means that if you put hours and hours into creating the best Amazon page, a counterfeiter can simply add his version under your listing and gain all your images, descriptions, reviews.