and what stops the amazons of the world from paying the ai provider, and getting your ai to buy from them instead of the best deal? How are you going to check and verify you got the best deal?

In the recent past, there was a browser extension called "Honey", which purported to find and apply the best coupon code for you when you online shopped. Turned out they were actually (amongst other things), in cahoots with the shops by ensuring that you get only a modest discount, rather than the best available coupons (and this was paid for by the shop).