Amazon gives non-Prime members free shipping at $35 or more of eligible items. Instead of simply letting users get the product with free shipping, they’ve added a discount that prices it exactly one cent below the $35 limit, while only subsidizing the price with $3.38, which is about half of what they’ll then charge you for shipping.
It might be your physical address. I’m not sure how long youve lived there but maybe someone who lived there before you ran a bunch of charge back scams or something and got put on a list somewhere. If that is the case then your address plus prepaid card and privacy respecting email will throw up red flags for any retailer that uses that list.