That is the situation right now at Walmart. Kellogg's Corn Flakes are $3.28 for an 18oz pack. Great Value (Walmart own-brand) Corn Flakes are $1.43 for the same size package.
In the Sold By Amazon program, it sounds like there wasn't a volume minimum or an actual purchase-for-resale going on. The inventory isn't on Amazon's balance sheet at all, if it doesn't sell then that's someone else's problem financially.
It’s complicated for Walmart, because there is documented evidence of them telling suppliers what wholesale price they will _accept_, but that does not change that it is ultimately Kellogg’s wholesale price that is being met by Walmart.
I mean, Walmart could just choose not to sell Kellogg's Corn Flakes at all. If that was more profitable, I'm pretty sure they'd do that.
They sell their own brand at a lower price point for price-sensitive customers, they sell the "premium" brand at a higher price for customers who buy on the basis of the name etc.
Additionally I believe Amazon was pricefixing in cooperation with other retailers.