There is a very good chance you are getting cookie stuffed (lol):
Basically a website you have visited is secretly adding cookies to your computer tied to their affiliate link.
This means that if you buy products on amazon within 24 hours of getting cookie stuffed, the person who stuffed you is collecting a commission (in the neighborhood of 4-8%, depending on how prolific of a stuffer they are).
They are probably using The Kind Diet because it seems so innocuous that no one will suspect malicious behavior. They aren't hoping to sell you that book but rather just want to tag along for commissions on whatever you happen to buy. Naturally, this sort of thing is against the rules, so if you report this to amazon maybe you'll get whoever is doing it banned.
The likely culprits for this are adult, warez, pharma, or gambling. Always use protection when browsing the dark side of the web, else you're gonna get stuffed. Coupon sites also do this a lot. If something says "click here to reveal your discount" - obviously you don't want to click that.