In case others were as confused as i was about this "While they’re often confused, Sold by Amazon and Fulfilled by Amazon are two different things. With SBA, Amazon prices your products and owns any transactions that take place. When an item sells, they pass the proceeds on to you for allowing them to sell your product. With FBA, you price your products and own the transactions. It is a service where Amazon handles t…
Another thing Amazon does these days is real-time delivery time arbitraging on top of real-time prices. You may see an item be delivered by some date X, only to see minutes later it is available to be delivered by date X-2. To them it's another lever to pull.
They must have some game theorists/economists working on this.