ASIN is the main way, ISBN/EAN/GTIN the secondary you interact with their API. All those affiliates make heavy use of that (e.g. when you go to our website and click on a camera datasheet, we show, if available, the details of the product on sale at Amazon). Affiliates are a big part of Amazon marketing, they can’t just cut that off for questionable returns.

they can't; thats how you authenticate you are purchasing the right book for classes, etc.